One of my biggest regrets, in the way I left the WTBTS, is I didn't have a backup plan...the people I moved in with were great...at first...slowly we got on each others nerves and within a few months I was looking for another place to live. With little money I ended up sleeping in the college parking, showering in the gym,  and gathering aluminum cans for food & gas money. The college I chose didn't have dorms. Eventually I found a room to rent and got back on my feet, but I will never forget those three months.
Does the school you are going to have dorms?
Other than that I have to agree with everyone here about how to break the news...you are a better judge of your family than we will ever be...my mother was/is psycho, so I sneaked out. I think my dad knew, but he never let on, he still had to live with her after I was gone.