The story of a family of dwarves snatched from the gas chamber by Josef Mengele himself sounded incredible. But how to verify the testimony of Holocaust survivors? And should you even try?

'I was saved by the grace of the devil," Holocaust survivor Perla Ovitz told us. Again and again, she recounted in detail how she and her family were taken to the gas chamber and ordered to strip naked. A heavy door opened and they were pushed inside. "It was almost dark and we stood in what looked like a large washing room, waiting for something to happen. We looked up to the ceiling to see why the water was not coming. Suddenly we smelled gas. We gasped heavily, some of us fainting on the floor. With our last breath we cried out. Minutes passed, or maybe just seconds, then we heard an angry voice from outside – 'Where is my dwarf family?' The door opened, and we saw Dr Mengele standing there. He ordered us to be carried out and had cold water poured on us to revive us."

The Ovitz family, from the village of Rozavlea in Transylvania, was the largest recorded family of dwarves: a dwarf father who sired 10 children, seven of them dwarves. Perla, born in 1921, was the youngest. In that remote part of Romania in the early 20th century, it was difficult for anyone to eke a living from the land and livestock, and impossible for someone standing less than 3ft tall.

Their mother, anxious for her children's future, guided them towards a common skill, a profession in which they could together make a living and would be neither isolated nor ostracised. As the five sisters and two brothers were all good-looking and musically gifted, the stage seemed the perfect choice: for where else could they be applauded, courted, honoured?

Throughout history, dwarves had been entertainers, often part of a circus or vaudeville show. But the Ovitzs wanted the stage all to themselves. They appropriately named their musical ensemble the Lilliput Troupe, and for 15 years had a flourishing career in central Europe. Their two-hour show consisted of popular hits of the day, skits and music. Perla had a tiny, four-string pink guitar that looked like a toy, her sisters Rozika and Franziska played on quarter-sized violins, Frieda struck on the cimbalom, Micki played both a half-sized cello and accordion, while the energetic Elizabeth took on the drums. Their elder brother Avram was the scriptwriter, actor and general manager.

The Ovitzs lived a communal life in one big house in the village. When any one of them got married, the spouse moved in and joined the enterprise. While the dwarves basked in the limelight, the average-height family members worked behind the curtains as stagehands and wardrobe mistresses. It was the only all-dwarf ensemble with a full show of their own in the history of entertainment.

When the Nazis came to power, the Ovitzs were doubly doomed: under the Aktion T-4 euthanasia programme, the Germans set out to kill people who were physically or mentally disabled, whose lives were considered "unworthy of living", "a burden on society"; and, as Jews, the Ovitzs were the target of the Final Solution.

On 19 May 1944, they were brought to the Auschwitz-Birkenau death camp because they were Jews. But, by a twist of fate, their disability played for them. It was rare that one person from an entire family survived the camp, let alone two, but all 12 members of the Ovitz family – the youngest a baby boy just 18 months old, the oldest his 58-year-old dwarf aunt – emerged alive.

Listening to the unimaginable horrors of Holocaust survivors, you shrink, stunned. But historians are reserved about oral testimonies. The witness may get the timeline wrong, forget facts or infuse memories of others into his or her own. Close to the event, the witness often finds it difficult to convey details of the trauma they endured. Crucial events can be forgotten, and trivial ones take centre stage. Consciously or unconsciously, shame and guilt can obliterate vital facts.

The Ovitzs leaving Auschwitz-Birkenau in May 1944

We embarked on the trail of the seven dwarves of Auschwitz with the notion that we would subject their story to the same rigorous examination that would be applied to any other historical source. So we not only collected their testimonies, but crosschecked them with those of dozens of other survivors, inmates and doctors, either first-hand or in archives and libraries. We unearthed medical documents in Poland and Germany. Still, we followed the advice of Professor Yehuda Bauer, a Holocaust historian and himself a survivor, that "one must never argue with a survivor".

Descending the ramp at Auschwitz-Birkenau, the seven dwarves and their five average-height family members were immediately separated from the others in the transport. They were told to wait for the arrival of Mengele. In rotation with other physicians, he was sending the multitudes to their immediate death, and selecting the few fit enough for slave labour. He was also using his long shifts on the ramp to pluck out twins, as well as hunchbacks, hermaphrodites, giants, dwarves, obese men and corpulent women – in general, anyone suffering from a growth disorder.

On the night the Ovitzs arrived, Mengele was asleep in his room at the nearby SS headquarters. All the troopers on duty at the ramp, however, knew well of his passion, of his collector's mentality. To gain favour with the freak-hunter, they were always on the lookout for new specimens to enrich his "human circus". While a lone dwarf did not provide reason enough to knock on Mengele's door in the middle of the night, seven dwarves, along with their tall siblings, seemed good cause for disturbance.

While the SS were brutal towards the newly arrived, they were cheerful with the dwarves. Realising this, two families from the Ovitzs' village approached and told the officer they were related. The Ovitzs kept silent and did not prove them wrong. Now they were 22. Mengele hurried out to see his new acquisitions. He was delighted: "I now have work for 20 years," he exclaimed.

A black army truck took them to a building at the edge of the camp. They were pushed in, stripped naked and smelled the fumes. The event indelibly etched the imminence of death not only on Perla's memory; three other members of the group, whom we interviewed, as well as Elizabeth, Perla's sister, who wrote her memoir, all attested that they were beginning to be gassed and would have died if Mengele had not suddenly reappeared.

Though we had five first-hand eyewitness accounts, we wanted to verify the story. The only way to do so was to study the procedures and manuals of operating a gas chamber. These were designed to kill between 500 and 2,000 people at once, depending on the size of the hall. Cyclone B was effective only at a room temperature of 27C, which was achieved by cramping a mass of people together. Gas chambers were simply not operated for merely 22 people; small groups were shot.

Furthermore, according to the camp's rigid safety orders, SS personnel had to wear gas masks when operating Cyclone B. Although the victims died within 15 minutes, the SS men routinely waited half an hour before turning on the powerful fans that dispersed the gas from the chamber. Only then were the doors opened. The operators themselves did not enter; instead, Jewish inmates from the Sonderkommando were sent in to drag out the bodies for cremation. Once the extermination process had begun, it could not be halted, because by then it would have been impossible to open the doors.

What actually happened was that the Ovitzs and their neighbours were taken to the camp sauna for disinfection, where the water poured over heated stones produced much steam and fumes, as well as temperatures intense enough to cause someone to faint. The sauna had a particularly traumatic effect on both small children and fragile dwarves that might easily have created the impression of being gassed.

And what about the appearance of Mengele at the door? They regarded him as their saviour, and there were several later incidents in the camp when he indeed rescued them from imminent death at the hand of one of his rival doctors. So, for the Ovitzs, every narrow escape that they had in the camp was thanks to him.

Mengele had several hundred twins at his disposal, and he carried out notoriously cruel experiments on them that led to countless deaths. But he had only one family of dwarves, so he was careful not to put his precious guinea pigs at risk. He gave them special living quarters and their food portions were larger. Their hair was not shorn, because he needed it for his experiments. They were allowed to wear their own clothes, because prisoners' uniforms did not fit their bodies. Former inmates told us that they thought they were hallucinating when they saw a colonnade of seven dwarves dressed warmly and elegantly, as if for a Shabbat stroll.

In the research on twins, Mengele was the field worker for his mentor, Professor Otmar von Verschuer, in Berlin. But he was looking for a research niche of his own and he found it in dwarfism. Mengele was aiming not only to discover the biological and pathological causes of the birth of dwarves, but to demonstrate the racial theory that in the course of its long history, the Jewish race had degenerated into a people of dwarves and cripples.

Members of the Ovitz group described to us in detail the painful blood-taking that they underwent. Often they fainted and water was poured over them to revive them, only for siphoning their blood to resume. Medical science of the time was obsessed with blood and its constituents, and it was generally believed that plasma contained all genetic traits. But only the medical records, all bearing Mengele's flamboyant signature, clarified what he was looking for: signs of kidney problems, liver function, typhus and syphilis.

Written accounts of inmate doctors shed further light on the endless anthropological measurements and comparisons between the Ovitzs and their neighbours, whom Mengele mistook for family. The doctors extracted bone marrow, pulled out healthy teeth, plucked hair and eyelashes, and carried out psychological and gynaecological tests on them all.

The four married female dwarves were subjected to close gynaecological scrutiny. The teenage girls in the group were terrified by the next phase in the experiment: that Mengele would couple them with the dwarf men and turn their wombs into laboratories, to see what offspring would result. Mengele was known to have done it to other experimental subjects.

Inmates in Auschwitz-Birkenau tried to improve their lot with whatever talents they had. A barber would hope to shave a kapo (prisoner supervisor) for a piece of bread or two cigarettes; a seamstress might mend the block elder's clothing; a painter would get a piece of sausage for making portraits for the SS guards; and one champion chess player was kept alive to play with Mengele.

Professor Israel Gutman, an Auschwitz survivor and prominent historian, recalls that "feasts and saturnalias were celebrated at kapos' and block elders' quarters. The artistic programme consisted of obscenities and dirty jokes. Sometimes a prisoner with a sweet voice would sing prewar hits in various languages. The kapos especially favoured melancholy tunes. The famous stars were very popular among the kapos and enjoyed a special income, thanks to their art."

Perla (right) and Elizabeth Ovitz: as the five sisters and two brothers were all good-looking and musically gifted, the stage seemed the perfect career

However, Perla Ovitz insisted that she and her family never took part in the "nightlife" of the death camp: they never performed in these drunken revelries, never sang in public nor entertained parties of kapos and SS men. She did remember one event. Sunday 30 July 1944 was the fast of Tishah Be'av, commemorating the destruction of the Holy Temple in Jerusalem. Being familiar with the Jewish calendar, Mengele perversely ordered the leader of the women's orchestra to prepare a special concert to desecrate the holy day. Perla remembered that the programme consisted of romantic, melancholy German songs that moved her and her sisters to tears as they watched the performance from their tiny stools in the audience.

Yet in her autobiography, Playing For Time, singer Fania Fénelon remembers it entirely differently: "We start with a foxtrot, Mengele waving his hand, the dwarves filling the stage, some couples dancing, other participants only managing a kind of grotesque, depressing twist. The men bow with a touch of servility; the women follow. Their jewellery, silk, ornaments glitter in the sun, igniting thousands of sparkles, dancing, swinging, intermingling. These creatures emit joyful sounds, trying to sing along with Clara, Lotte and me. They have high shrieking voices. The orchestra plays a march and they accompany with clapping and stamping."

Against the bleak backdrop of the death camp, the concert was so vivid that it became deeply etched in the memory of the survivors whom we interviewed. Isaac Taub was part of a group of twin boys enlisted to carry chairs and benches and arrange them in rows. The teenagers were allowed to stand at the back during the performance and Taub clearly remembered the Ovitzs on stage. "We all knew that the dwarves were performing for the Nazis."

Yet Perla denied that they ever took part. As pious, God-fearing Jews, the Ovitzs deemed performance in Auschwitz to be an abomination, like singing and dancing in a graveyard. Nor would performance under coercion have lessened their shame – not with a painful awareness that while they were entertaining Nazis, the chimneys never stopped smoking. No wonder they strove to erase their experience from their history, and their minds.

Death was the master of Auschwitz and its toll was piled outside for all to see, like so much garbage waiting to be collected. A space suddenly empty in a bunk did not shake heaven and Earth. Those who survived the night walked about as if wrapped in an invisible shell, praying to live one more day. But the Lilliput Troupe drew the inmates beyond their shells, to care about them and their whereabouts. Subsequently, many survivors referred to the fate of the dwarves in their own memoirs.

In her autobiography, Auschwitz: True Tales From A Grotesque Land, Sarah Nomberg-Przytyk describes in appalling detail the horrible death of two members of the Ovitz group, one of them an 18-month-old baby boy who died as a result of one of Mengele's experiments: "Around him, like pillars of stone, stood a large woman, along with the child's mother, slim and frail; the three midgets sat in miniature chairs." In the evening, the dead toddler was placed outside the block with the other corpses to be taken to the crematorium. Nomberg-Przytyk also recounts the death of Avram Ovitz, the leader of the group: "The old midget wanted his wife" and tried to slip through the barbed wire; a guard spotted him and, when Avram got close enough, shot him. "He never made it to his wife."

But the little boy and his uncle Avram were not killed, and lived to see liberation day. What, then, caused Nomberg-Przytyk to make such grave mistakes? Most likely she was compressing a number of events, and attributed to the dwarves two common occurrences in the daily life of the camp: the death of a child in his mother's arms and the shooting of an inmate who approached the electrified fence.

And there were others, such as Renee Firestone, who described the death of the Ovitz dwarves: "The Germans found a community of midgets, transported them to Auschwitz, shot them en masse and then were forced to let them sit in a pile for three days until the crematoria could take them."

One plausible explanation for the discrepancy between fact and remembrance is that the survivors, who regarded their own deliverance as miraculous, found the chances slim that someone as helpless as a dwarf could escape death. The fact that the Ovitzs were transferred several times from one side of the camp to the other caused their fellow inmates to lose touch with them, and in Auschwitz, when you stopped seeing someone, it could mean only one thing.

The seven dwarves, as well as their entourage, all survived the war, and emigrated to Israel in May 1949. Three months later, the Lilliput Troupe was back on stage. In 1955 they made their last bow, but dwarfism did not affect their life expectancy. The first-born, Rozika, reached the age of 98 and her sister Franziska died aged 91. Perla Ovitz died in September 2001.

• Giants: The Seven Dwarfs Of Auschwitz, by Yehuda Koren and Eilat Negev, is published by the Robson Press at £16.99.