Dad's vision & hearing are greatly impaired. He has a CPAP machine, which he uses at night but sometimes takes off when we wakes early AM or in the middle of the night. He often will sleep past noon unless we wake him up. Yesterday we celebrated his 92nd birthday in the evening. I let him sleep until he woke up about 2pm. He seemed more clear-headed when he'd slept that long. Is there anything to be concerned about with him sleeping so much?
He'll also often say he's not hungry, but will eat when food's put in front of him.
This all seems like a natural process of slowing down.
If he has a busy day one day, he will sleep more the next.
All in all he is in bed up to 18 hours a day.
So I do not think your dad is sleeping excessively.
Perhaps for the next big family event you could do it in the afternoon. That is what we do for Dad now.