Dear musician,
First of all, you need to ask yourself this question. Did you join the band because you wanted to play music or to get together with friends and have fun? If all you want to do is just play music, I would recommend you to change then because you will not be able to play a lot of music with our sister always argue. Alternatively, you could try to talk with them and understand why they're always arguing and try to resolve it. I'm really sorry to hear about your problem and I hope you can figure it out.
Best
