If he's going to continue this crap about going to things he was previously invited to by your family, and your family know the current situation, I think it would be entirely reasonable to ask them to message or call him to say Fred, we know you and Sowhat are seperating. To be clear, you are not invited to xyz events.
I'd ask the wedding couple or their parents to do the same if you're close enough to them. Or call and cancel the hotel booking, make another one he doesn't know about, and leave without him.
This is just him continuing the abuse, you realise that don't you? Ask your friends and family to help protect you from him.
I'd also, being absolutely honest, ask your biggest male realtive at the bbq to take him aside away from the kids, give him his car keys / call him a cab, and tell him quietly to leave, right now. You all need to stand up to him or he's going to carry on with this shit. You've told the kids you're not going to be married anymore, you can explain that will mean you will be doing things seperately, so Daddy will go to see Granny, Grandpa and Uncle Mark without you, and you will see Nana, Auntie Sarah and Grandad without him.