Family In law drama

My SO and I have began the long process of ttc, I love my partner very much but his grandmother is another problem she is very arrogant woman, when we first got together she would text his ex partner, who put there child up for adoption without his permission ( he absolutely frowned upon contact with her after this) she then proceed to constantly throw it in my face about there relationship, I had accepted at one point in our relationship we may have to take his son on but his ex partner was by far no means ok with a criminal record a history of drug and alcohol abuse I really was not ok with her still being in our present. MIL was very understanding as she had undergone a very traumatic time with the ex partner. I have made it clear to my SO I do not want anything to do with his grandmother who is a very self obsessed, rude mean old lady. But is it too far to ask she not be around her great grandchildren when the time comes?

I'm not looking to hurt my SO other and wonder if it's over stepping a line so to speak..