The eight are Nathan Law, Finn Lau, Mung Siu-tat, Kevin Yam, Anna Kwok, Dennis Kwok, Ted Hui, and Gong-yi.

They are all accused of various offences under the 2020 National Security Law, related to their participation in (legal at the time) democratic processes.

Each has a bounty of One Million HKD on their head, and all reside outside of Hong Kong and China

https://www.theguardian.com/world/2023/jul/04/exiled-hong-kong-activists-in-uk-defiant-about-hk1m-bounties-for-their-arrest

Exiled Hong Kong activists in UK defiant about HK$1m bounties for their arrest

Nathan Law, Finn Lau and Mung Siu-tat vow to continue speaking out after ‘unprecedented’ move