From minor Corsican noble and artillery officer to statesman and military leader, Napoleon Bonaparte’s many incarnations continue to fascinate historians and the public. Now, a rarely seen collection of miniature portraits of Bonaparte and his family could reveal a more intimate side to the warmongering emperor.

The items are among 44 lots, still held directly by Bonaparte descendants and estimated to be worth just under £1m, to be auctioned in Sotheby’s annual Treasures sale of decorative arts in London.

Henry House, head of furniture and decorative arts at Sotheby’s, described the miniatures as a family album from an era before photographs. “These are intimate personal portraits that have been passed on within the family,” he said. “We see Napoleon’s father, mother, brothers and sisters, and in-laws; it’s a remarkable group of items being presented at the same time. These portraits are how they see themselves in the family, rather than how they want to be presented to the public.”

Most of the well-known portraits of Bonaparte and his entourage were propaganda tools aimed at establishing the family as a hereditary dynasty along the lines of the Bourbon kings, overthrown by the French Revolution.

House says there is an enduring fascination for the man nicknamed Boney by the English: “He was a pretty amazing man who came to France as an immigrant, became emperor and had an incredible dynasty that stretched across Europe. There’s an enduring mystery and romanticism about Napoleon, similar to that of a rock or film star who dies young.”

Bonaparte was taken prisoner by the British, with whom he had sought asylum after the French turned against him following his defeat at the Battle of Waterloo in June 1815, and sent to the remote south Atlantic island of St Helena. Among the personal effects he took with him were a collection of 33 mainly tortoiseshell snuff boxes, many set with portraits of close family members.

Two being sold this week portray Bonaparte’s father, Carlo Maria Buonaparte, a descendent of minor Tuscan nobility who had moved to Corsica, and his mother Maria Letizia Bonaparte. Another snuff box bearing Bonaparte’s portrait was given to General Henri Bertrand, one of his most trusted aides, who joined him in exile on St Helena and was at his deathbed there on 5 May 1821.

The gold-mounted tortoiseshell snuff box, with a portrait of the Empress Josephine by Pierre André Montauban, Paris, 1806-1809 (est. £80,000-100,000). Photograph: Sotheby's

Among the most exciting items going under the hammer, says House, is a gold-mounted tortoiseshell snuff box with a portrait of the Empress Joséphine wearing a gold chain hung with an even more miniature portrait of Napoleon (estimate: £80,000-£100,000). She is depicted holding a letter dated 2 December 1806, announcing his victory at Austerlitz, which she had supposedly just received.

Another small box from Joséphine’s collection shows portraits of her two children, Eugène and Hortense, from her first marriage to Alexandre, vicomte de Beauharnais, who was guillotined during the revolution. Despite having no blood links with Eugène, Napoleon considered him the most capable of his relatives and formally adopted him, sending him off to command the army of Italy and naming him viceroy. Hortense married Bonaparte’s brother Louis, king of Holland, and was the mother of Napoleon III, also known as Prince Louis Napoleon.

Living in different European countries and separated from their mother, they remained close to her and mediated on several occasions in Joséphine and Napoleon’s tempestuous relationship.

Sotheby’s says the items come directly from descendants of the Bonaparte family but the seller wishes to remain anonymous. They are believed to have been passed down via Eugénie de Montijo, the last French Empress, who was married to Bonaparte’s nephew, Napoleon III. The couple spent their last years in Britain.

An exhibition on until November at the Musée des Beaux-Arts in Arras, France, called Napoleon: Images of the legend, features more than 160 works from the chateau at Versailles. It includes one of several versions of the most famous Napoleon painting, showing him on a rearing horse, called Bonaparte Crossing the Alps by French artist Jacques-Louis David.