And therein lies a complication: You might be dying of cancer but be a socially skilled person. And your visiting brother might be healthy as a spring baby, but as socially rude/unskilled as ever. Who is now the more challenged part - you might be dying of cancer, but you are still better equipped socially to wrangle your brother and the situation, than he is. I'm not saying we should tolerate that brother, but precisely his 'social cancer'/lack of ability to handle his (social) interactions leaves him with 'chronic social cancer' as well.
This goes too for whenever you are helping someone with solving their problem - are you helping them in a sensible way, relatively to how they are challenged - often we end up fighting the 'victim' as we smother them with 'advice'. ("Well you only have this problem because you refuse to do what I told you to do earlier" yada yada).