Trying to reason with a drunk or a dry drunk is an exercise in futility. I'm afraid I don't have any suggestions other than to say "no", walk away and don't discuss it at all. What he wants to plan for himself is fine -- go ahead! No need for you and your son to have to deal with any of that.
Call and make sure any credit cards have a very low daily credit limit on them -- it'd be terrible if he started actually buying these tickets on your dime.
