Is my point valid for refusing to donate a kidney if my brother were a drug addict sibling?

My mother's aunt is struggling with her first, oldest child. He was a drug addict and is now a 50ish year-old man on dialysis. His mom takes care of him and he hasn't worked for years. My father thinks either his mother or his 4 siblings should've already donated a kidney. I agree with the mother part but not with the siblings risking their lives for a drug addict.

My father thinks a sibling should donate out of principles regardless of them being drug addicts. I disagreed. He said then stated it can even be for my son. I feel that's different. I would donate for my son (I'm now a mother) regardless of the reason, not for my brother. He thinks it's the same. No it's not the same; a brother and a son is different. I have no obligation if my brother (an adult) makes bad choices in life. I feel responsible for my son no matter what. I never want to bury my child. Isn't my point valid too?

I think that man's 4 siblings are within their rights to refuse and choice what they want to do with their bodies. It's not their obligation to save their older brother from unhealthy, destructive path. What do you think?

Is my point valid for refusing to donate a kidney if my brother were a drug addict sibling?
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