I'd honestly NOT worry about the girlfriends parents!
They're the ones should be embarrassed to have raised such a greedy selfish woman with no shame.
But I apply that also to dss parents (not you)
They didn't turn out this way by happenstance
I'm not sure he understands how hurt we are.
Then he needs to be told!
If my dd (20) EVER behaved like this to her dad and stepmum I'd go through her like a TON of salt!
And my ex is a deadbeat piece of shit! Still no excuse!
And dd knows I would too!
Wtf his and her parents have played at raising them I do not know. Like fuck would any child of mine behave like that and get away with it I don't care how big they are.
IF she did I would be making damn sure she apologised to all concerned and acknowledged the hurt and distress and worry all this mess had caused.
This is the kinda thing my sister would do. She was COMPLETELY mollycoddled and spoilt by my parents especially my mum and this is exactly the kinda crap she'd try to pull.
But she didn't get to being that way as an adult with good parenting. All through childhood whenever she fucked up it was excused and minimised and that's continued into adulthood.
Long term I think you need if you can (and I acknowledge it shouldn't be your responsibility!) to get through to your husband that if he even gives in a little on this - and I mean the behaviour NOT just the money - then he is not doing his son any favours.
His son needs to learn the world owes him NOTHING! He wants a big ass fancy house in his mid 20's best he gets his arse into a well paying/long hours job and pays for it! Same goes for the girlfriend (who sounds a petulant little madam anyway)
Honest to god what a pair!