How do I help my father cope with his mother's death?

Help him to make some good memories in the time they have left - little things like games of scrabble, looking through photo albums together, get her to tell you all those secret recipes and write them down. Take some photos of you and other family members into the hospice - your grandmother's memory may be affected by her medications, and being in a new place will unsettle her. Take morning tea in with you to share together. You sound very mature for your age. The best help you can give is to be yourself and share your youth and love of life with your Dad and Grandad to help them remember that life is an ongoing journey, they will absorb some of your happiness even if they can't feel any themselves.