Family member got 关押 in China due to proselytizing

I was told I need to get a letter from us (the family) before our friends in China can engage a lawyer to get family member out. I was also told I should fly out to China to engage a lawyer which imo is too expensive for me and I also dun know how to engage a lawyer in a foreign country.

What other cause of actions should I undertake?

If we don’t do anything does it means once the police has done their investigation they will release them?