What should I do??

So I've been living with my bf for a little over five months now, along with his parents, plus his younger brother and his gf.. My bf has had his own place before but his parents hated it so he moved back (he's 21 I'm 18) now it was pretty good at first, until his little brother who is my age had his new gf move in... Everyone hates her.. She has a bad personally, she's extremely hard to live with already and she is just a bad person. It's so bad that I am considering moving out. I don't know how to tell my bf or his parents bc they have already talked about that not being a good idea. They have also talked about kicking the other girl out and even their own son bc of how bad they are together. So idk what to do.. Find somewhere else to live, which won't be easy right now. Or just allow this other girl to take over my life and take advantage of this household. No one will say anything to girls face about how crappy so idk.. Any advice?