FMIL's Aunt can't go due to some other trip she has planned, so she GAVE HER INVITE AWAY to her daughter and son-in-law. They were not invited because FMIL has a HUGE family and if we invited one of her cousins, we would have needed to invite all of them. So today I got their "yes" in the mail and had to txt a pic to FI & FMIL asking if they knew WTH "Mr & Mrs. X" were since they were not on the list, and I've never heard of them. FMIL got to the bottom of it, and seemed to have no problem with it.
I'm not going to say anything about it, but you can bet that if there are other cousins pissed off that those 2 attended and they were not invited, I'm going to let FMIL deal with it.