Family Drama

In the last year, my FSIL cheated on my FBIL while he was deployed with the Army. While what she did was not ok, I am keeping my opinions to myself and staying out of it because it’s really no ones business but theirs. They have decided to stay together and work on fixing their marriage.

The problem is, my FH wants to ask his brother to be one of his groomsmen, but doesn’t want to invite his SIL at all. His entire family has decided that my FSIL is an outcast who is not welcome at any family gatherings despite the fact that they are still together and trying to fix their problems.

I don’t want to rock the boat and piss my future in laws off, but I don’t think excluding her is the best course of action, as it might cause his brother to not want to attend, and if they are staying together the family should at least try to be civil. Am I wrong? Should she be excluded?