B.T.
Maybe this compromise process will work. I sincerely hope so. You obviously need to communicate clearly with your folks what your expectations are, your needs, your wants; you also need to ask for theirs, so that it's a two-way street, this communication thing.
But in the end, if this doesn't work, I suggest you move heaven and earth, do whatever necessary, to get separate housing, so that you can get control of your child again. The parents will be gone before you are finished rearing him, being responsible for his well-being, and that MUST be the top priority. You cannot let him get comfortable disrespecting you, disobeying, ignoring you, for though it may be slightly cute right now, when he is 16, it will be a nightmare. He needs consistency and structure. All kids do. That's our job as parents. When they don't get it, they are thrown into a huge disconnect, feeling that since no one else is in charge, no one else is acting as leader, much as Cesar Milan describes a dog needing a pack leader, the child will begin to take that on, and they obviously can't do it very well, having no perspective, no life experience to draw on when decision-making. So everything falls apart when they try to be parent and decision-maker by default because no one else is.
Get on top of it, and stay on top of it. Also Google The Role of Sugar in Health (it's nonexistent!) and give your parents articles to read. Ask them to consider the research coming in on the fact that sugar interferes with the immune system's feedback loop, interferes with the DNA's gene expression switching system. It has huge implications for a child, in resisting disease, in cell development during growth, all kinds of mishaps possible.