I have had sleep cycle problems my whole life, luckily there are tons of things he can try!
It is important to talk to a doctor, and rule out conditions like sleep apnea that might also be affecting sleep. A doctor can prescribe a sleep study to see what happens when he sleeps.
A person does not necessarily need continues sleep to get there required sleep for the day, for instance he could try sleeping twice a day for four hours, or three times a day, etc. It is probably more important to sleep at the same times each day though, so the circadian rythym does not go into a random cycle.
Also, natural sunlight during the day, avoid as much artificial light as possible, and only sit in the dark when it is night or time for rest!

For the sweets, the obvious would be to not buy them in the first place, so they are not around to eat! If he has problems with sweets, it will most likely be something that everyone in the house has to give up! Sugar is addictive, so anyone bringing home sweets would be fueling his addiction!

There are many healthy alternatives that taste sweet, and might help satisfy the need, but are still healthy!
This is something else to talk to the doctor about, have him refer you to a dietitian (or some sort of professional), who can direct you on what foods are out there, types of meals, etc. You can even get help with grocery shopping, things like what to look for on labels, or how to shop healthy within a budget, or even how to cook the meals!

If he is allowed to exercise, I would also recommend a personal trainer! A trainer can develop a exercise program taking into consideration his issues, and help to motivate him threwout the workouts.