Is it sinful to not keep ties with family?

As-salamu alaykum, I've been struggling with my siblings lately. My older sister has been rude for months - little arguments, shouting, and I noticed she only talks to me if I say Salaam first or needs something. So I stopped greeting her first to see what would happen, and now it's been about four months since she's spoken to me except to ask me to move in the kitchen or hand her things. It hurts more because she's the most religious of us, she even finished memorising the Quran. My younger sister also causes problems with the younger siblings; she picks fights and bullies them when our parents aren't around. I always step in to stop things, but she can be very hostile. She's polite to outsiders but cruel at home. She's an adult and has gone long periods not speaking to our older brother - once for 2.5 years. I try to patch things up before they drag on, but sometimes my studies consume me and I can't handle all the drama. The longest I've let things go unresolved with her is about three months. I keep making dua that we improve, but the situation seems to be getting worse. I know the Prophet (peace be upon him) encouraged keeping family ties and not cutting off relatives beyond three days, but what can I do if they're actively avoiding or fighting me? And is it true that our good deeds aren't accepted if we don't maintain family ties? Any practical advice on how to approach this kindly, while protecting my own wellbeing and fulfilling my duties as a Muslim, would be really appreciated. JazakAllah khair.