The other day I had a.......?

Maybe call your brother up and ask how they felt about the "intervention" , they may have realized that their fighting could make others uncomfortable. May I point out that you seem to blame the sister in law for all of the arguments, so if she is so hard to deal with, maybe your brother could benefit from talking to someone about how to handle her little displays of anger. If she doesn't get help, then god help them who have to deal with her, right?