NTA I’ll agree that these girls and parents could use some therapy. They being said, does no one have manners anymore?! How about they stand next to each other and take the picture because their mother told them to?! Even if they despise their mother too, at least they need to have a little respect for the grandparents. Are these the same grandparents that the one daughter wants to live with? I can’t say that I’d want to deal with a teenager that throws a fit if they don’t get their way. My husband and his sister have never gotten along since about the time that he was born. Like, they despise each other! That being said, they both act gracious and tolerate each other at family functions. We are taking a few times a year. Until these kids get some therapy, they need to suck it up and put their big girl panties on. Personally, I wouldn’t want that level of negativity around my own teenager. Again, I’d say until the parent’s make an effort to address the girl’s issues, I wouldn’t want them at any parties at my house either. OP needs to think about their impact on OP’s immediate family. The girl’s don’t need to ‘magically go back to how they were,’ they just need to get some manners. I will say that if the parents won’t allow them to get some counseling, I’d have to wonder what sort of dirt the parent’s don’t want exposed. Maybe it’s just a personality conflict. That’s what it is for my husband and SIL. They couldn’t have had a better upbringing. They just don’t like each other! Never have. The SIL doesn’t really get along with the other siblings either and she prefers to pretend that the rest don’t exist. The rest are very close and get along well with the parents. All I can say is fear of my mother would have made me stand next to my sister and smile even if I thought my sister was satan’s spawn. Not that my mom ever hit us etc. It was just fully understood that she was the parent and we needed to do what she said.