I've been going through the same thing with my Nsis.
We live in different states, but she does live near some family members of my stepdads. My stepdad will talk to one of them and has to hear stories about my mom.
It amazes me how she can tell all these stories when we don't talk to her.
Not sure what my stepdad tells them, but I hope he tells them that we don't talk to her so how could she know anything about my mom or any of us for that matter.
I tell people that there are 2 sides to every story and they are only hearing one side. That and I don't talk to her so how can she know anything about me.
Other family members (besides stepdads family) now don't ask about her anymore at christmas. They used to ask every year.
Good luck just keep up the NC eventually they will stop. At least most of mine have. You can't worry about what others say. I always change the subject as fast as I can.