My best friend throughout my teenage/college years (we're still friends but live a literal ocean apart) had a saying for this that I use to this day, "I'm not going to let your problem become my problem."

Children are exempt from this as they're not fully formed and constantly affected by their environment, particularly their immediate environment.

Adults who act like assholes and just say, "that's the way I am" while refusing to even try to change (e.g. discuss things, go to therapy) are jettisoned ASAP from my life. As difficult and painful as that expulsion may be (it is your wife, sister-in-law, sister... are you noting a pattern here?) in the long run I've come out much happier in every instance.

Not just happier but with much more time to spend on things to help me grow in positive ways. I don't know about other people, but I really underestimated how much TIME dealing with all that drama takes, not to mention the emotional energy.