Oh boy that is upsetting. It would be one thing if he never offered in the first place but you cant offer something like that, tell the other family members they are all set, and than not follow through. I think you might need to say that nicely to him if you havent allready. Maybe forget the fact that he is mister money bags and put it in terms that he would relate to, like "I know this is a lot of money for you and we appreciate it, but we should book the flights now and pay the room balances off to insure that x y and z can definitly come before things get too booked up, if it is a matter of not having the time to do it, than we would be willing to book it if you want to give us your debit/cc #".