OK, so FMIL tells me today that a couple she insisted on inviting at the last minute (that RSVPed yes) just told her that they have 2 weddings the day of my wedding, that they rsvp'ed yes for both, and that they are planning to come to our ceremony and cocktail hour and then leave to go to the other wedding. FMIL said she was speechless and didn't know what to say. I told FMIL that if they were not going to stay for dinner I prefer that they not come, because our caterer will still charge us the full per person price (which is quite high) for these guests, and they will miss 90% of the food and that it is wasteful. FMIL's response was that she felt bad but doesn't feel she can say anything, but that she knows they will give us a very generous gift. Now, I normally in no way expect guests to follow the "cover your plate" rule, but the fact is we are choosing to use a very high end venue/caterer, and even a very generous gift may not cover the cost for these two guests. I just feel that it's wasteful and disrepectful to know ahead of time you are going to miss 70% of a wedding and then rsvp yes anyway. I don't know if there's anything I can do but I'm just annoyed.