I must have very low expectations of my family. It never even occurred to me to expect my family to use my chosen name (although in fairness, I didn't start using it offline myself until I was in my early 40's). I can't even get them to stop using the hated short form of my given name my parents assigned me, and almost no one else has called me that since I was 18. That said, other than my mother, I barely interact with my family, and they pretty much have no interaction with the rest of my life.

All that said, LW has made it clear that this is important to her, and for them to ignore her wishes is, as Prudie says, perverse. It's a bit like my sister sending me mail to "HatedNickname Spouse'sLastName," when she knows perfectly well I didn't take his name, and that it aggravates me, only on a scale of about 10x worse. I think Prudie's advice is good. There's not much else that's going to get through them.