Story highlights Far fewer Yazidis are trapped than previously feared, officials say

Sisters Aziza and Dunya Hamid escape mountain in a helicopter rescue

CNN's Ivan Watson tracked them down at a makeshift shelter in Zakho

They found out their father, who stayed behind, was safe

Theirs were the faces that stood out in the chaotic helicopter evacuation off the Sinjar Mountains.

Tears streamed down the cheeks of 15-year-old Aziza Hamid and her 17-year-old sister, Dunya, who were among a lucky few to fight their way onto an Iraqi helicopter, a scene captured this week by a CNN crew on the flight taking food and water to thousands trapped by extremist fighters.

Two days later, CNN's Ivan Watson tracked the girls and some of their family members to the third floor of a derelict building in Zakho, Iraq, a makeshift shelter where roughly 1,000 Yazidis with nowhere to go have taken refuge.

Inside, the girls, their brothers and their 16-month-old cousin are confined with their meager belongings to a few feet of bare concrete.

"You no have food. You no have drink. You no have sleep. It is very, very poor," the girls' brother, Kareem, told Watson on Wednesday. "It's no good."

Aziza Hamid, 15, was rescued from Mount Sinjar and now lives in a derelict building that houses more than a thousand other refugees.

A portrait of Aziza's family.

Photos: Yazidis rescued from ISIS Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – An Iraqi gunner opens fire at possible ISIS targets during a rescue operation by the Iraqi Air Force and Kurdish Peshmerga fighters on Monday, August 11. The dramatic operation at Iraq's Mount Sinjar involved taking supplies to desperate Yazidis and even bringing some aboard a helicopter to make it safely out of the area. Hide Caption 1 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – A CNN crew was on the flight, which took diapers, milk, water and food to the site. Thousands of people have been fleeing from the militant group ISIS, which has taken over large swaths of northern and western Iraq as it seeks to create an Islamic caliphate that stretches from Syria into Iraq. Hide Caption 2 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – A couple dozen civilians were rescued during the operation. CNN's Ivan Watson, who was on the chopper, described the mission as "heroic." Hide Caption 3 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – An elderly woman is put on the helicopter. Hide Caption 4 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – Yazidi people sit on the aircraft with members of the CNN crew. Hide Caption 5 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – An elderly Yazidi man cries after he was rescued. Hide Caption 6 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – A toddler named Helen sits in her mother's lap after being rescued. Hide Caption 7 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – Rescued civilians sit on the helicopter. Hide Caption 8 of 9 Photos: Yazidis rescued from ISIS Yazidis rescued from ISIS – Yazidi people arrive safely to the Kurdish territory. Hide Caption 9 of 9

Their plight, like so many, began more than a week ago when they fled into the surrounding mountains when ISIS fighters stormed the town of Sinjar.

Thousands are believed to be on the mountain, trapped without food, water or medical care in the summer heat.

U.S. President Barack Obama ordered targeted airstrikes last week, partly to protect the Yazidis and others fleeing ISIS. He also ordered humanitarian airdrops.

A mass evacuation of Yazidis is unlikely following an assessment by the U.S. State Department and military that found far fewer people were trapped than previously feared.

Once believed to be in the tens of thousands, the number of Yazidis in the mountains is "now in the low thousands," Brett McGurk, a deputy assistant secretary of state, told CNN on Wednesday.

Part of the reason for the drop in the number trapped is the airstrikes and humanitarian airdrops, as well as Iraqi helicopter evacuations, McGurk said.

For now, those escaping continue to do so either by helicopter or a treacherous journey on foot.

ISIS fighters have vowed to kill the Yazidis, calling them "devil worshipers."

Photos: Iraqi refugees fleeing ISIS Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Yazidi family from Sinjar cleans a spot for themselves in a derelict building that houses more than a thousand other refugees on Thursday, August 14, in Zakho, Iraq. Hide Caption 1 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A woman and child sit in the makeshift housing on Thursday. Hide Caption 2 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Yazidi woman holds her baby while crossing Peshkhabour bridge from Syria back into Kurdish-controlled Iraq on Tuesday, August 12. Hide Caption 3 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Entire families carry nothing but the clothes on their back. Some are barefoot. And not everyone who set out on the arduous journey survived. Hide Caption 4 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – The militant group ISIS, which now calls itself the Islamic State, executes civilians who don't adhere to its version of Sunni Islam. Hide Caption 5 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Yazidis fled into the barren and windswept Sinjar Mountains more than a week ago after ISIS captured their town. Hide Caption 6 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Descendants of Kurds and followers of an ancient pre-Islamic religion, Yazidis are one of Iraq's smallest minorities, and have been persecuted for centuries, but they have a strong sense of community. Hide Caption 7 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – According to some accounts, Syrian Kurds also helped people use parts of northeastern Syria under their control to reach Kurdish areas of northern Iraq. Hide Caption 8 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A young refugee carries a disabled man across the bridge. Hide Caption 9 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Thousands trudge across a river to seek humanitarian aid in Syria. Hide Caption 10 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A number of those who made the treacherous trek off the mountain told CNN that PKK fighters control parts of the mountain, and they fed and protected them from ISIS. Hide Caption 11 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Kurdish border guard watches while people cross. Hide Caption 12 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A senior Kurdish official estimated that as many as 70,000 people remain trapped on Mount Sinjar, and that at least 100 have died so far from dehydration and the heat. CNN could not independently confirm those estimates. Hide Caption 13 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A man weeps after been reunited with his family. Hide Caption 14 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Kurdish Peshmerga stands in front of the bridge. Hide Caption 15 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Children rest after arriving back into Kurdish-controlled Iraq. Hide Caption 16 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A little girl was seen crossing the bridge by herself. The United States is sending more troops to northern Iraq, a move that U.S. officials told CNN is necessary to help in the rescue of tens of thousands of Yazidis trapped in the mountains. Hide Caption 17 of 17

JUST WATCHED Will ISIS attacks spread to U.S.? Replay More Videos ... MUST WATCH Will ISIS attacks spread to U.S.? 01:49

JUST WATCHED ISIS massacre survivors speak out Replay More Videos ... MUST WATCH ISIS massacre survivors speak out 03:18

JUST WATCHED Thousands of Iraqi Yazidis flee to Syria Replay More Videos ... MUST WATCH Thousands of Iraqi Yazidis flee to Syria 02:21

JUST WATCHED Thousands of Iraqi refugees flee ISIS Replay More Videos ... MUST WATCH Thousands of Iraqi refugees flee ISIS 02:55

Yazidis, one of the world's smallest and oldest religious minorities, are members of a pre-Islamic sect with its roots in Zoroastrianism. It has ties to Hinduism, Christianity, Judaism and Islam.

When ISIS advanced on Sinjar, an ancestral home for many Yazidis, the Hamid family was forced to flee.

"I was happy we survived, but I was sad and worried about my father," Dunya told Watson.

The girls' father, like so many, refused to leave their hometown of Sinjar ahead of the ISIS advance.

"We all tried hard to convince my dad but he refused to leave the house," the girls' other brother, Thabed Hamid, said.

"He said it would be a humiliation. I decided I couldn't let them capture girls and the women. So we left."

The family didn't make it far in their car before they ran into ISIS fighters, who were shooting at fleeing Yazidis on a bridge.

"I jumped out of the car and off the bridge," Aziza says, "because I was scared of ISIS."

From there, they made their way up the mountain in the sweltering Iraqi summer heat.

"If we were able to find a tree where we could rest in the shade, we were lucky," Dunya said.

"For the first four days we had no food, only water. Any bread we found we fed to the little kids to keep them alive."

It would be days before they learned their father's fate.

On Tuesday, they learned in a cellular telephone call their father was still alive.

He escaped Sinjar and is on the mountain, the girls told Watson.