And what exactly is stopping you from living with your grandmother? You can still do it, you're legal, and just b/c now your parents decided that you can stay, doesn't mean they're chaining you up to the bedpost. You can be the grown up and say "I'm sorry mother, but *I* made my decision. I think it's time all of us take a break from each other." And frankly, you should give both you and your parents time to miss each other. It's obvious you have issues to work out, but if living i nthe same house isn't working, then being away is the best choice. Give yourself time to miss them, to see if you miss them, and for them to have a house without you, it may make them cherish your presence more.

Me and my mm get along fine most of the time (in fact we're almost attached to the hip) but there were time in the past where living together was impossible. She was making me miserable, it was awful, I couldn't stand the fighting anymore. So I took my things and planned a week away (the first time I spent a week at a friend's house in a city 9 hours away, in a different state, the second i spent a week at the beach with a couple of friends, 2 hours away from our city) and things were much better when I got back. It gave both of us time to miss the other, to not be able to reach the other at all times, to just be away, it was a relief.

You and your parents don't seem to be particularly close, but the abscense seems to be a good idea, specially in your case. Stay away a month with your grams, ask her to let you stay for a little while. You need to be away from them, and not in a stay out all day and come home at night, you wont have to come home at night and face your parents.

You don't have to move out, just take some time for yourself.