Aww bless you, everything will be fine!
I think it's fine for you to chase the people - I'm assuming they've been aware of your date for a while so have had plenty of time to find child care. I would give them a final deadline, a few days before you need to know for food confirmation. Tell them if they haven't confirmed by then, they are still welcome to the evening if their childcare allows, but unfortunately you won't be able to cater for them during the day. That should give them a kick. If they can't be there, who cares, you'll still have a fab day without them.
That's great that your man is helping - I know it's hard, and I'm so guilty of trying to do everything myself, but try and trust him.
Take a deep breath, go for a walk, make sure you take a break from wedding stuff every so often.
It will all be worth it in the end, and you'll have an amazing time, but do come and rant whenever you need to!
Good luck. X