Some of the family members are being held in detention camps, some have been sentenced to prison, some are being held in jails and the whereabouts of others are unknown, Mr. Mahajan said.

Their detentions were first reported by The Washington Post.

The Chinese government keeps tight control over information about Xinjiang, the far western part of the country, and reporting in the region can be extremely difficult. Mr. Hoshur worked as a reporter there before fleeing in 1994, after he reported two stories that angered officials. He is now based in Washington, where he learns details about little-known episodes in Xinjiang by calling police stations and demanding answers from local officers.

In 2014, his three brothers were arrested, apparently in retaliation for his reporting. One brother, Tudaxun Hoshur, is serving a five-year sentence for endangering state security. Rexim Hoshur and Shawket Hoshur, who were released in 2015, were detained again in September and are being held at a re-education camp.

Mr. Hoshur has said he would not quit, despite the pressure, because so many people had taken great risks to pass along information from Xinjiang. “I cannot leave,” he told The New York Times in a 2015 interview at Radio Free Asia headquarters in Washington.

Ms. Hoja said in a statement posted online that her brother Kaisar Keyum, 43, had been detained in October, and that she had not been able to reach her parents, who are in their 70s, since late January.

A relative of Ms. Hoja’s in West Virginia told her that she had been warned against staying in contact with her. “I am the reason that around 20 of my relatives were arrested by the Chinese police,” she wrote.

Mr. Juma said his brothers Ahmetjan Juma and Abduqadir Juma had been detained in May. Abduqadir, who has heart and other health problems that require medical care, is being held at Urumqi No. 1 Prison in the capital of Xinjiang. Ahmetjan’s location is unknown.