One of my FI's family RSVP'd for 3 when only two were invited. They have several children, but I think the 3rd person they included was one of their children (who are all grown up, in their late 30's/early 40's, but one may still live with the parents). I had to severely limit my guest list in order for both of us to have equal numbers of guests, but my FI wasn't so careful with his initial list that he even actually forgot some of his family. He ended up adding close to 10 guests days before we sent out the invites (we ended up dead even on guests after the additions).
Though it's just one more person, and may have been my FI's fault for forgetting, how should I approach him to handle the situation?
Any advice? Thanks so much!