Kind of hypothetical, kind of not. If your brother or sister in law does something to (emotionally) hurt your sibling how do you treat them? Do you hold a grudge on your sibling's behalf or act like nothing has happened as it is nothing to do with anyone else?
For instance, my closest friend and I have an unwritten rule that we don't judge each other's DHs based on what we tell each other, but that is because we both know there are usually two sides to every story and our dh's good points far far outweigh their bad points.
However my sis has just found out that her dh has a 'love child' who is 5 years old, was born just before they got together (from a one-night stand or something). BIL didn't know, though he did find out a year ago. My sis found out a month ago when they received a letter demanding 5 year's worth of maintainence and the woman and child turned up on their doorstep.
Now BIL didn't know, wasn't going out with my sister at the time. But he did hide it for nearly a year, probably to protect my sis who was pg at the time, but has also told other lies to cover up how long he had known.
Hopefully they will get through it but I don't know what to say to him. We are not close to them at all, see each other once or twice a year as they are overseas. My mum has had words with BIL but it's not my place to is it?