I have already said I will have a party that he doesn't have to invite his family to or attend himself - he has said no to this.
But he's just said no and that's that.
No. He does not get to just say no and that's that. That is very much not how a relationship works, and if he thinks that it is, then you will be very unlikely to still want to marry him. Houses can be sold.
I suggest you make this very, very clear right now.
Don't be tempted to brush this off. This doesn't actually have anything to do with his parents. You've already quite reasonably made a few suggestions as to that, including not involving them at all in which case they'd meet at the wedding, as he prefers. Fine. You are accommodating and compromising with him on the thing HE is not happy with.
But that's not enough for him. A good partner (a good, reasonable person full stop!) would at that point meet you in the middle and say, yes, sorry but I wouldn't want to have them both at a house party. But obviously, fine for you to go ahead and have a party without them there.
But no. He wants complete control and thinks it's then ok for him to forbid you from having a party AT ALL. Nothing to do with his parents.
Not ok. Controlling, twatty, unacceptable.
Don't marry a person like this.
If this is the first time you've seen him try and throw his weight around, I suspect it's because now the house is safely bought he thinks he can get away with it, whereas before you could - and would - walk away.
Houses can be sold.
Divorce is expensive!