oh mama... i hope you and your family are never exposed to this toxic family again.
i have to tell you, i think that anything gained by having a relationship with these people is totally overshadowed by the harm it is causing you, your DH and your kids.
i would not continue to participate in this relationship in person. i would send letters (like our christmas update letter) and pictures, but i could not let my kids go there. if it was very important to m DH, i would go with him t o support him, but leave the kids at home (with someone who will love, respect and care for them.