What warrants cutting off family?

Last year my BIL and SIL got a divorce and it has been messy. My BIL has had a girlfriend through the divorce who has caused nothing but problems. A few months ago the new girlfriend and my BIL got into a physical altercation 5 states away and she called my MIL during their fight and told her “f**k your son, f**k you and f**k his kids” Then proceeds to call his not even ex wife yet and tell her the exact same thing. The girlfriends sister then proceeds to message everyone in our family asking for my MIL phone number. I respond and tell her I wasn’t comfortable giving out her number and then she proceeded to tell me “that’s why you can’t have kids you hoe ass bitch and you’re going to die trying” The girlfriends whole family was out “looking” for us and we felt threatened.

The whole time my BIL is sitting by letting this happen. Letting her family speak to us in such horrible ways. His girlfriend is cussing our whole family and is being extremely disrespectful. None of us had anything to do with the argument they were in. It was personal problems that they drug us into. But now they are coming down to visit but I want to cut all contact with them both. My in-laws seem to think it’s wrong that I don’t want any contact with them anymore. I’m willing to hear an apology from my BIL only if he is willing to give one and I’ll be around him ONLY for my husbands sake to see his brother. But I don’t think I could ever be around his girlfriend again. She talked so horribly about my nieces and has caused so so so many issues. This was just the worst one. But is this enough to cut contact or am I being sensitive?