Sounds like behaviour in my family too.

Haven't spoken to/seen my brother in over a year, all because of his wife's behaviour. There appears to be a different moral compass operating with most of my close family. Do I want to be part of it, no. I want to look in the mirror and see an honest person, not a hypocrite.

Only contact I have is with my 17 year old niece (my brother's daughter). She has more decency and integrity than most family members (incl her parents). Even my aunt has got involved in the politics.

You are right in not going off at your sister. You are rising above her poor behaviour. Having other issues, it's not just because she can't handle being around sick people.

Look after yourself and take solace in having one relative that does care about you