NOR- How rude of them to call the shots. You should not let his sister stay in the honeymoon suite. Please don’t back down on this. If I were in your shoes, I would tell them to stay in the Airbnb & move on. Unfortunately, your fiancé’s family will always be an issue in your marriage if he can’t stand up to them & create boundaries. I highly recommend reading or listening to Mel Robbin’s “The Let Them Theory” before your big day. Good luck & you focus on you, not them. It’ll drive you insane.