Restraining Order

My sister and her husband moved into my dad's home a few months ago. They have children age range 6mos-10yrs. My bro, dad, my son and I have lived here for years. They constantly have hostile arguments and have brought domestic violence into the home with their frequent fights. All of us are fed up and have called the cops but they can not do anything unless she cooperates and asks for help herself. The cops told us to file a restraining order on BIL for the hostile environment due to the fights. That may be a way to get him out according to cops. I'm not even sure if this would work out as he has not been physically violent with any of us. Any advice, experience or knowledge on how this process may result? We live in California.

Forgot to mention, my brother overheard them fighting yesterday morning when my sister said to her husband "I have you on video threatening to hurt my family"