You shouldn't have any guilt about holding onto the bike even if it is too large for you to ride. Like plenty of others have said, maybe move the components over to a similar/same frameset in your size depending on their condition. Got any pics of your dad riding? Put one+ next to the bike/frameset to display.

At the very least you could move a water bottle cage over to one of your bikes that it would make sense on as a sort of homage. I've done that, sort of threads the old and the new together.