My dear, I think this is what we so happily call here at SI the KARMA BUS. Now you need to get off of it and stop worrying about what he's doing and start worrying about what you are doing.
He is on a Karma bus to nowhere and this woman will string him along til pigs fly. He will be left in a pile of crap with absolutely nothing.
You on the other hand, you are free from this drama. (he is still living it. Think about that!) But you are free. You don't have to worry about what he's doing anymore. Let him post on all of her kids FBs. You need to not check anymore. Seriously. It does nothing for you other than drag you down.
Please don't mistake what I'm saying. I do get it, but being on the outside, I can see that a lot of us WS become addicted to the fascination of all of the drama. We too need help from this addiction.
Stop checking their FBs. Block them. Trust me, when the sh!t hits the fan, you will know about it, but stop living through it daily or weekly.