I'm sorry that you cannot escape him right now. Would you feel comfortable blocking his calls and having someone else listen to any message he may leave? On my android phone, I went into the specific contact I wanted to block, pulled up the menu, and blocking the calls was an option there. He goes right to vm and I don't have to deal with him if I don't want to.
I've found that pulling away from abusive and toxic family is difficult. I have a really hard time with others in my family disapproving of the break even though they know the extent of his abuse. I'm sorry Also about dealing with the impending loss of your grandma (hugs)