I got to the table cleared my throat and made the "cut it out" signal. Then I asked to speak to her in the kitchen. I was pissed.
I told her not to talk about things like that with my kids anymore. That while yes, their sisters ARE their half sisters, we choose not to call them that. There are NO halves in our family. They are blood, they are family and that's it. She tried to argue with me and tell me I was wrong for teaching my kids that.
I finally said "Look. You can teach YOUR kids whatever you want. If you want to teach J, R and C that their brother A is different because he has a different dad then go ahead. But my kids don't need to think that way. I would appreciate it if I never hear you discuss this subject with them again".
We left not long after that.