JKS, Ugh! I really feel for you. My situation has similarities although OW isn't a known quantity and lives in another city so I don't feel like H's family is on her side.
In terms of the kids, my H also wanted to introduce them to OW now before we're divorced and before he'd moved out of the house. I have a provision in my divorce filing that prevents him from taking the kids out of state with my permission. I told him the only way I'd give permission would be if a counselor could convince me it was a good idea.
We got a recommendation to a great family counselor (expert on kids) who listened to our situation with a fresh perspective and told H what he thought. He told H that in no uncertain terms that it was too early to introduce the kids and he would risk his relationship and OW's future relationship with them if he did it now. The kids need to see our marriage end and accept that we aren't getting back together. He told H how even 20-30 year olds cling to the hope of their parents reconciling.
Anyway, I found the outside perspective to be very helpful. Not sure if you have the same leverage to get your H to agree to that.
I am finally at a level of detachment and H comes here and sees me being more social than I ever have been. He has commented on how he thinks he is looking worse and worse and I keep looking better and better. He's so entrenched with OW that I'm not sure it makes a difference, but I've done enough that I feel like if he ever changes his mind...he can see some changes. The very hard part for me was the changes he'd really want to see were more sexual/intimate and I just can't do a 180 on that stuff anymore. Last fall, when his A first started, I did...I do think it made a difference, but it also allowed him to be on a very comfortable fence.
Anyway, try to live life for you. You will come out of this a stronger, happier person in the end. Look for ways to focus on yourself and enjoy you!!!
M 44, H 46 D11, D9, D5 Married 12 years PA confirmed 9/2011 I filed 3/2012 H moved out 7/2012