We went straight into the parks on our recent visit, and by the time we got to the hotel the slots for breakfast they had left for the first couple of days were 10:00-10:30. We wanted 07:00-07:30 because our kids get up early, were told to turn up anyway because it wouldn't be busy and it wasn't of course. I'm sure your dad is used to coping with his diabetes, so a few cereal bars or something for emergencies won't be too far away. It all depends on what you call decent. I'd advise you buy a costume or 2 at home and pack them, they're going to be much cheaper and no worse quality.