That doesn't sound good hun!

Is your mum with you on this? Could you try together to get him eating healthier? Unfortunately I think if the parents aren't willing to make any changes though he doesn't have a great deal of hope - he'll learn all his lifestyle (eating/exercising) habits from them. Are they not watching that Jamie Oliver thing? They need something that will truly shock them, like the fact that if they don't look after their son they are essentially shortening his life expectancy (I know it sounds extreme, but if habits like these continue it will only get worse for him in future).

Sorry I'm not much help, but I do think if you can get your mum on side too as she spends a bit of time with him together you might be able to get somewhere