If we don't hire him he'll be invited to attend as a guest, naturally. If he takes a paid gig in preference to celebrating his parents' birthdays, that would be hurtful too. so let’s just get this straight.
you’re having a lavish party, lavish enough that you want to hire a band. So you have suggested that your DS plays, that you will play his band mates but that you expect him to do it for free as his gift to you, as gratitude for the fact you’ve (presumably willingly) funded him through university.
But that’s not enough. If you don’t hire him, then you expect him to attend anyway and feel him taking paid work rather than playing at your party, for free, and therefore not actually being a part of the party would be wrong. Never mind you weren’t actually intending to invite him to the party you just want him to show up to play presumably so you can do this party a bit more on the cheap.
I think you’ve got a bloody nerve, if I were him I would just say no to playing full stop, find some paid gig and stuff the party which you don’t really want him at anyway, you just know that it’ll show you up if he’s not there.
And all the posters calling him an ungrateful twat, he’s a professional. And the OP saying she’ll pay his band mates and not him is singling him out personally.
And her expecting him to attend her probably dull party for someone of his age instead of a paid gig is then leaving his band mates unable to earn that night either.
Nope. The OP is the one in the wrong here. If he’d demanded to play then fine. But he didn’t.