Great advice everyone. My thought was to talk with the elders. Perhaps even stalling your dad by saying you want to study more and get your service hours up....all lies just meant to buy you time.
While slowing them down by seeming sincere you could talk to your school counselor, find an alternate safe place to live and find some sort of job that would help you get ready to live on your own or with some roommates.
There's no easy answers when dealing with fanatics like the witnesses. Best of luck.