Peace,

Just catching up on your thread after being away for a few weeks. Ugh, I'm so sorry to hear about your H's terrible decision to marry ow. I'm sorry for your children, too.
You know your H best. If he doesn't look happy, he probably isn't. He definitely doesn't sound like someone who is happy and content with his decision.
This is your H's mistake to make. There is nothing that you can do. As for the kids, you don't need to force the issue of them meeting her and knowing who your H is. Like everything else, they'll eventually find out the truth. Do you really want to force this girl into their lives as a stepmother?
Hang in there and detach. This isn't about you. Your H is still a mess.