Lets just say first the brothers ex (or sisters ex for the girls) and they had broken up and you were both good friends, if you were together alone and they started on you would you let anything happen if you could help it or stop it? Lets just say whoever they are that they are decent looking.

Scenario two if friend you knew got dumped by their partner and the partner soon afterwards was sniffing around you would you go for it, ask how the friend is with it, leave it be...what?

Just curious. Has no relevance to my own life.

-With the sibling thing.... Eh, most likely no because I'd be stuck on thinking, "my brother kissed this chick, ew ew ew."
Plus, if they lived with you and you constantly had their ex over, probably would make them feeling shitty.

-The friend question, I'd evaluate how much they meant to my friend, if it would hurt them, etc.