If you all are still in therapy, maybe feedback from therapist on how to handle would be helpful? Maybe they could swing by for drinks/apps before or dessert after, excuse for others that they can't stay because they're doing the dinner part with her family this year? That might help keep it "normal" for the grandkids and other family not in the know, yet still limit the contact. It'll be hard, even for a short period. I'd be feeling pretty angry too... of all people, so incredibly disrespectful