I 24M Despise my girlfriends (21F) Family, what do I do?

For context Me and my girlfriend have been going out for a year now and my girlfriend’s family is so toxic when I’m not around, constantly getting into daily arguments with each other and always making my girlfriend sad daily. She has a 20F sister that I’m convinced has bipolar as she constantly tells my girlfriend how terrible of a sister and person she is but then goes back to being nice to her when she wants something from her.

Now after hearing all of this from my girlfriend, every time I go over to her house they put on a show and act as if there is nothing wrong and that they are completely normal, pretty much acting fake to my face all the time which makes me not want to be their especially when the sister is there because she has stopped acting fake when I’m over and been so rude to my gf when I’m right next to her. I’m also not allowed to say anything because her family thinks that she doesn’t tell me anything because it’s not my business.

Now family is really important to me and I’m worried that if I ever marry this girl that I’m gonna have to deal with these people and have terrible in-laws which is not something I want for my kids. But my girlfriend is the sweetest girl I have ever met and we honestly have nothing wrong between us.

I feel like I’m getting the short straw here as when I see my cousins and siblings with there girlfriends and all the time they spend with their partners families makes me really want that and unfortunately I just can’t have that with my girlfriends family

I think about breaking up with her and seeing if I can date a family friend that I know as a good family similar to mine, but then I’m scared to take that risk as it’s likely it won’t work out.

Not sure what I should do as I have serious concerns about the future and don’t want it to drag on any longer.

TLDR: I despise my girlfriends family as behind closed doors they are really toxic constantly arguing and fighting with each other but then when I go over they are normal except for her sister which is the worst out of them all. I think about dating a family friend that I know has a good family but it may not workout and I’m not sure what I should do in this current situation as I love my girlfriend but I worry about the future if these people become my in-laws and I don’t want it to drag out any longer.