I know its hard, when you love someone so much and they are stubborn. May the LORD reveal HIMSELF to your Grandfather in a dream. My Grandfather didn't accept JESUS until right before his passing.
May the LORD bless your Mom, for taking care of your Grandfather...and may the LORD provide a means for her to hear grandfather during the night.
May the LORD bless you and your family for caring enough to go and stay some with your Mom and help her with Grandfather.