I'm so sorry you are going thru this, thank goodness we didn't have kids we had to deal with in our D. I don't think your h is being fair to those kids! He needs to see them & he has to put their needs above his & the ow! Whether he does that or not, I'm not sure but he has to know how upset they are about this whole thing. I know it just makes you sick the thought of them being near her. It made me sick the thought of my h being near this ow, much less now marrying her & now with this baby. At the time I didn't know she was a sociopath. She is down right crazy!
At least he has agreed to take it slow, that is the best thing for now. Really, until your d is final they shouldn't be around her at all. You can really take him in the d, I don't know what state you are in but in my state it was supposed to be 50/50, didn't happen, I got almost everything even attorney's fees paid.
You try to be strong, I know, believe me I know it is much easier said than done.