Parenting Teenagers (12-18) Support Group
This community is focused on the joys, challenges and concerns faced by parents of teenagers (12 to 18 year olds). The major areas of child development include: physical development, perception and sensory development, communication and language development, cognitive development, emotional development and social development.
I think you've already done just about everything that you can do to save their relationship, and the rest is up to them. Perhaps in time, he will come to realize the irrationality of his new wife's erratic behavior, and acknowledge the effect its having on his other relationships. (Just think, if family is uncomfortable and doesn't want to be around, how is she around his friends?)
Until then, perhaps you can arrange an 'outing' night for them to spend time together, with just each other, and keep supporting 'them'.