So, I'm getting married in four days. Yesterday, one of my FI's friend's called to see if he could bring a date. A little background...when we sent out the invites we asked if he was seeing anyone (because last we heard he had a long-distance GF) but he said no, they had broken up. So he's coming to town (his hometown) for Christmas anyway, and will know literally half the people at the wedding, including the entire groom's family and all the groomsmen.
So yesterday, he called to say that his ex-GF was coming to visit, they aren't back together, they are just "buddies" (WTF?) and he wants to bring her. Umm...it's four days away. We already gave the numbers to the caterer, etc, and more than that, he doesn't seem to realize what an inconvenience it is to just add people (he didn't even give us her name). Now my FI's friends are pressuring us to let him bring her, because it's "not fair" that they all have dates and he doesn't. (They are all married, most with children, while this guy is stuck in adolescence perpetually.)
What to do?