That's right, I remember now. The therapist is part of the alienation problem.
have a therapy dog come and be present at the exchange as the twins love dogs. It might be a welcome distraction for them. And since the handler of the dog will be there as well maybe BPDxw will behave?
That sounds like a very creative and worthy idea!
Maybe build in a buffer for plan B and C in case the dogs don't work. Can your husband plan to spend additional days there?
Another possibility is to ask local law enforcement to make a domestic assistance call with your H.
I'm guessing there is no way to get a new therapist involved, even if it was a family therapist for your H, who might agree to meet with the kids after the exchange? It still amazes me how skillful and effective a good therapist is. My son's therapist is a miracle worker, helping us both see a way forward that neither of us could see before.
It might also be worth finding a therapist in your home town who will meet with the boys and your H. It's almost like, What does your H have to lose at this point?