We have a completely fucked up family. My SIL cut us out of her life, and my brother went along with it, and completely refused contact for 15 years over some imagined slight. SIL also cut off her own family. Once her kids got old enough, they left home and cut her off, so you know it’s all completely screwed up.
My brother decided to rejoin the family, but without apologizing. Just showed up one day and acted like the 15 years hadn’t occurred. When I was back in town, he stopped by my mother’s house. I confronted him about him raping me, my younger brother and others, and while he admitted he did it, he wouldn’t take responsibility for offer a real apology for it. I’ll have nothing to do with him.
So, it really depends on why the sisters are estranged. I wouldn’t invite them to Christmas if they have asked to not be contacted from the family, and may or may not tell about the cancer depending on the circumstances of the estrangement.
You’re (obviously) a better and stronger person than your brother by about a million orders of magnitude. Quite frankly, I feel really honoured that you’ve shared your story with us.
Remember that blood is not really thicker than water. You have no obligation to care for someone who has done you that kind of wrong.