Absolutely right.
This man beat her until she couldn't sit down. And clearly the mother must have known about this abuse. What on earth is this poor mother-to-be worrying about hurting the feelings of Grandma who didn't defend her own child from the hands of her father.
OP - I was in this position with an abusive stepparent and worried about upsetting my mother. I wish I had realized sooner that my first and only priority was to my own child and (sorry) but to hell with upsetting your mother. She chose to stay with an abusive man who repeatedly abused you both physically and mentally. 
Protect yourself, protect your child, protect your family. Do NOT (for goodness sakes) thank this  man for bringing you up. Stand up for yourself and listen to your gut. Your gut is telling you to keep Grandpa at arms length. Go with it and best wishes to you.