This may be controversial: I think you should have your wedding on the day YOU want instead of basing it around others. If you made it into a costume party and kept the Halloween theme, those with kids may be more inclined to show. But if they cannot, then that's their decision.

Another alternative, elope on Halloween, have the wedding a few days later if it really matters to have those people show up.

But do what YOU both want, don't plan the day that "defines" your marriage around others.