FH has an aunt and an uncle that are apparently considering coming to just the rehearsal dinner on Saturday and not the wedding on Sunday. They're not in the rehearsal at all, but FILs are in charge of the RD and they've decided to invite around 50 people, mostly family. So it's not strange that they would attend the RD in general, but to not attend the wedding? My first thought was that it's really pretty rude, sort of says to me "we'll go to the RD because it's on a Saturday, but not the wedding because it's on a Sunday."
Are there any etiquette rules about this that I'm unaware of? I can see why they would do that I guess but it doesn't sit right with me.