My father is 85-years-old. He sleeps all day and all night in 3 or 4 hour naps. He sleeps for a few hours then watches TV or reads a book for a few hours then falls back to sleep.
He also eats very little. He will have a cup of coffee and a Muffin/ then have half a sandwich/ then have a few Crackers and crab dip for dinner.
Nothing you've mentioned seems very unusual in itself - it's whether it's comfortable for him or not, really.
I think a thorough physical exam is in order. Does he have a PCP he likes? If not, I suggest trying to find a geriatrician for him. (They specialize in old age the same way pediatricians specialize in childhood.)
In my mother's case, she would eat cookies, cake, or candy, two or three times a day every single day, and nothing else, if I didn't fix meals and put a small portion in front of her.
The love of sweets is also common, I am told.
I do agree that it's a good idea to get him checked out by his doctor.
I agree that it would be a good idea to look for a specialist anyway, though; not least because when something changes you will need help, and then it's much better if you can call on someone who knows what is normal for your father, and whom your father already knows. Choose your geriatrician carefully - you want someone who is conscientious and thorough, but wary of tinkering.
And how are you? Are you managing all right? It is very pleasant for us to read of a contented, undemanding, unproblematic gentleman living peacefully in his daughter's home - but that doesn't mean we don't appreciate that all the same the responsibilities can take their toll.