I am so sorry to read about this. I just lost my father on September 25th to Stomach Cancer. My father was in Hospice for 9 days.
Honestly, some people rally for quite some time. My father was alert and able to talk for the first 3 days in hospice, after that his pain was being managed by large doses of morphine, so he was basically in a coma. My father also had a J Tube that drained the fluids from his abdomen and bowels. Long pauses between breaths, a gurgling sound when breathing, and basically sleeping all of the time are signs that the end is near. Hallucinations, picking at the sheets on the bed, and spurts of energy are also common. My father died very peacefully. He took one big breath, and it was over.
This is a very crucial, and special time. It's ok to say goodbye, and let them know it's ok to let go.