Welcome, Damian.
I am DF'd as well as one of my brothers and mom has shuned us since around 1997. She also shuns my sister who was never Df'd, she just DA'd. The woman has not even met all of her grandchildren. Very sad. I stopped trying to get through to her a long time ago but every once in a while I get the urge to contact her. It sucks but really there is nothing I can do to change the situation short of returning to the cult in good standing. Ain't gonna happen.
Good luck to you. And I agree, your grandpa needs to be reported to the police if he is driving drunk. He is a danger to himself as well as innocent by standers.
BFD