i feel for you... i was there when my granfather passed too, but we knew it was coming. it was scary to see the last few minutes of life, and there is nothing you can do. I left the room when they took his body, becuase i knew that image wasn't an image i wanted to keep in my head. to say the least it was a humbing experience.
but you don't have to say anything to your family, everyone deals with everything differently, just you being with them says alot!