Basement with Kitchen in SF

[Richard Ma]

   Hi, i  have a  question about house that have kitchen in  the  basement. My parent rented their basement down stair to two family with no written lease  and it  got a kitchen down stair the house is located in SF, which tenant has more power over landlord. My parent have some problem with one family but have a good relationship with the other family. My concern is that the family that my parent having issue with will sue or not pay rent  to my parent. Is there anyway I can help my parent with this? or there's is no way of helping them and if they sue or not pay my parent, my parent have to pay them? I heard from my coworker my parent have to pay each person at least 10k each person. I just hoping to try to help my parent with this issue. thanks