It's okay... Go ahead and vent...
My father was similar. One of my JW friends told me when I was a teen that she thought my dad was "so nice!" I stared at her in astonishment; he might have fooled HER, but I was the one being hit, kicked, slapped and insulted - even knocked out at one point - by that vicious man posing as a "loving Christian".
Actually, if your father is anywhere as nasty as mine was, it might be a GOOD thing that he won't have anything to do with your children - it protects them from being indoctrinated into the cult by "grandpa"...