“Can we get past this, for the children?”
I would want to respond ……Which ‘we’ are you referring to?
But because you are about to give birth, I would concentrate on yourself, with the support of your fantastic family and not respond at all. Your new baby is priority and you must keep yourself on an even keel as much as possible for a good few weeks now.
OP, he and his OW are abhorrent. The timing is cruel, - quite wicked in fact.
You are quite right to do what you can to stay calm. This means ignoring his callous, cowardly and completely useless attempt at communication.
You are simply too busy with your impending birth to deal with his hideous behaviour and you are within your rights to not want him anywhere near you. (If that’s what you do still want)
Keep him hanging as long as you like. His question isn’t worthy of your energy. You owe him nothing. You aren’t obliged to dance to his cheating tune at all.
Don’t let him spoil your birth experince any more than he already has, make it as special as you possibly can.
You sound like a very strong woman ….you will keep it together for your babies.
All the best of luck to you OP.