HONG KONG—At dawn, officers from Hong Kong’s national-security police burst into the apartment of Derek Yuen and Eunice Yung, the son and daughter-in-law of a high-profile pro-democracy campaigner who criticizes China’s Communist Party from perches abroad.

The police seized a laptop and mobile phone in the raid last Monday and took Yuen and Yung, who is a pro-Beijing politician in the city’s legislature, to a police station for hours of questioning about the activities of their dissident relative before releasing them without charges, according to Yung.

Elmer Yuen, the 74-year-old U.S.-based activist who is the focus of the authorities’ ire, is one of eight overseas critics of China who are facing arrest warrants in Hong Kong after being accused of national-security crimes. He appeared at a news briefing in Washington last month and another in London on Tuesday, discussing his plans to form an unofficial government in exile.

Elmer Yuen, who shares his political commentary in lengthy videos posted online, said the authorities’ actions against his family members were intended to pressure him to speak out less and to halt his political efforts.

“Of course I worry about my safety and that of my family, but our work has a goal, and a price must be paid,” he told The Wall Street Journal. He said he wouldn’t be deterred “even if they arrest my entire family.”

The family and the widely diverging politics of its members have been the subject of public discussion in Hong Kong in recent years. They appeared in a 2020 documentary aired by the city’s public broadcaster RTHK, and their story has resonated with many Hong Kongers in politically divided homes.

Yung is the vice chair of a major pro-Beijing political party. Her husband once joked that their daughters’ crayons at home were missing a yellow one—the color of the city’s pro-democracy movement—because his wife had removed it.

After Yung was questioned, she said she was cooperating fully with investigators and hoped her father-in-law and the other dissidents would be arrested soon. “If I know about his whereabouts, I will without a doubt disclose it,” she said.

Yung and her husband didn’t respond to requests for comment.

Hong Kong’s chief executive, John Lee, has encouraged friends and relatives of the wanted dissidents to share tips and said they were eligible, along with other members of the public, for a reward of about $128,000 for capture of each activist.