Does anyone think that the family of a gf or bf has a direct impact on your relationship?

I have my issues but I get angry every time I'm around her brothers and mother..... The mom is rather large and lazy and both of her boys have autism.... I'm not making fun of them but idk. Also theu live in filth with 14 cats.... Does anyone have any ideas. My gf treats me like a king she does anything for me why do I feel angry a lot of the time?