That's very sad. He's lucky he's got you and your DH in his life.

Sorry in advance for the coming comment, but his parents sound like complete idiots if that's the reason they've disowned him. Now, if he'd sold their house and valuables out from under their feet without their knowledge, I could possibly understand it. But not for a silly thing like the location of an engagement party.
I think that its very unfair to call them idoits... You don't know thats the only reason. Keyhole judging try not to do it...