It seems your parents are jumping to the conclusion that either the Watchtower Bible and Tract Society -- a publishing company created by man -- is the church of Jesus Christ (Jehovah), or there is no God. The third option, of course, is that Jesus is still the Christ, the Redeemer and Savior of mankind and the Son of the Father, and that your parents just took the wrong path.
Uh...blowing your head off would seem to me not to be the next option. Your parents should be able to explain why a God who has revealed Himself throughout the generations of man, suddenly became the passive player in how He deals with man. If two or more of the Governing Body had heard from God, or if the early Bible Students had visibly seen what was, to everyone else, invisible (and I don't mean seeing with their understanding), they would have had some claim to what they were telling others. But they should explain why a church founded by men, indoctrinated by men and guided by men in today's world should be the same church founded by Christ, who visibly appeared after his resurrection and spent forty days with his disciples. If they cannot establish the legitimacy of the church, how can they expect anyone to follow the dictates of its founders, who are men?
To say that either the Jehovah's Witnesses are the true faith or that God doesn't exist is a substantial non-sequitur. I would think the universe being ruled by cows is still a few rungs up from blowing off one's head. If your parents say that their faith is the true path, then let them explain to you why that is. Jesus never taught the shunning of anyone was of him. He never did it to sinners, so why should your parents or any other Christian?
Get a good King James Version and throw away the NWT.