I have no experience with this topic, so hopefully I don’t step on your toes.
It does read like your mother is trying in her own way. Maybe there is a chance to talk to her alone without your father and explain a couple of basics to her? She probably has no idea what it really means and this is her way of trying, even if it is hurting you. Not saying it is OK, just that it probably needs time and good talks to process and accept it.
Maybe ask your grandma for her opinion on how to deal with her.