How to get along with in-laws sibling?

I am in a 4+ years relation with a girl who I really like and we have engaged 2 months ago. I have problem with her sibling's personality. they are loud, snobbish, not very smart and super happy (maybe pretending) , I am calm and try to find a corner to read my book or surf internet. I got in fight with the little one who always act like a 5 years old kid, she is 18. I actually told her to shut up when she was singing a Christmas song. she is very noisy. her father got angry and then we insulted each other. everyone blames me. they say I am a toxic person. I have to see her family once or twice a year and stay in their house for a few days since we live far from each other. now I think our relationship is in jeopardy. I don't think I would ever be able to get along with her sibling and she loves to spend time with them. Is it over for us? should we separate? I also agree I am not super tolerant and only like to spend time with people who I have something in common.