My father went into hospice with end stage renal disease. No more treatment was possible and was essentially filling up with fluid. They didn’t give him pain mess but did give him atropine.it eased his labored breathing enormously and may have some sedative properties. Being there with him..and your sister will bring you closer. That can be very comforting. I wish you well and send prayers for your Dad.
Like a another person said, having that conversation with your dad is good for you as well as him. And I also told my dad that it was okay to go; He had been a great Dad. Tell him that you and your siblings will be okay and will look after each other