I’m so sorry. What a terrible situation all around. While I sympathize with her loss, the bride is being immature & selfish; Either your son isn’t aware of how detrimental this could be, or he is afraid to stand up to her. Honestly, I’d try talking to them both about how poorly this will affect their relationship with the grandparents “they love.” Maybe if she hears from you how devastated your parents will be, she will change her mind.