My mom loves my kids but …

My mom got married to someone when my siblings and I were teenagers and we NEVER had a good relationship with him. Now that we are older and out of their house we don’t speak to him at all, I talk to my mom everyday and he gets upset about that and tells her that she needs to stop talking to me so much. I have kids and when they get into an argument he’ll tell her that my kids aren’t his grandkids so she needs to stop bringing them up. Today my son was talking to her on FaceTime and she showed him a picture. She said “This is me and this is your grandpa” I moved the phone and asked her not to tell my kids that he is their grandpa. He doesn’t like me and when he gets mad he doesn’t like my kids so I damn sure am not going to have them thinking that man is their grandpa. We called him Mr. Dennis when we were younger so I asked her not to do that and told her that they will be calling him Mr. Dennis like we did. She said “When they’re at my house they will be calling him grandpa” and I asked if she can respect me and not confuse them by having them call him that and said “Like I said, when they’re at my house they will be calling him grandpa”. I never had a relationship with any of my grandparents so with her being there for my kids is wonderful, but now I don’t want to let them go over there without me because she is not respecting me. Am I wrong for that ? When I was younger she made sure not to have my siblings and I around people who didn’t like her, I am doing the same thing but because it’s her husband it’s different 🤔 That’s not fair.