Address: No.2 Chengbei Road, Suicheng Town, Suixi County, Zhanjiang, Guangdong Province
If two people have entered the detention center, they should inform their close relatives in writing of the reasons for being detained within a few days after entering the detention center.
Your sister can't see your brother-in-law even if she knows the address of the detention center.
You can find a lawyer to intervene in the case, understand the specific case and defend your brother-in-law.