Advice needed

Y'all, I'm so angry and I need some advice on how to proceed without losing my mind. I am currently 33W2D pregnant, and my temper is at an all time high lately. When I turned 18, I separated myself from my parents for being very toxic and abusive people towards me, and I saw no way I would ever be able to get anywhere good without leaving. I have 2 younger siblings that they allowed me to keep in touch with, one who is now 17 and the other is 13 and has autism. Fast-forward 3 years and I am now married and pregnant, but my views towards my mother and step-father remain the same. All of a sudden, my mother decided that i can no longer talk to my siblings unless i allow her in my child's life as a normal grandparent. Now, in a normal situation, had she not manipulated and told me to either defend myself or be quiet about what happened at home, I would allow it. But, since she did those things for many years of my life, I am enraged! How dare she use my younger siblings to manipulate the situation into what she wants it to be, especially after so mucn time passing. I understand it being her choice on whether i am allowed to speak to my siblings, as they are her children, but i cannot believe the audacity she has to use her children to get to my child! Am I over-reacting to what she is doing? Or does my reaction make sense?