I've thought so much about you and this today.
Here's what I think I landed on:
You have every right to do what YOU feel is best for YOU and the kids.
If that is having the party, have it.
If that is canceling the party, cancel it.
If that is moving the party to your house, do it.
If that is bringing Arnold Schwartzenegger... well, he may be otherwise occupied, but if you want to bring someone whose sole job it is to keep Ex away from you during the party -- do it.
Do not for a second concern yourself about what people are going to think.
People are going to think whateverthehell they damn well please.
Regardless of what you do.
And that includes the kids. If it's a disappointment to them, they'll get over it.
Go with your gut and stay safe. (((hugs)))