Alan, welcome to the Forum. Man to be 18 again. That would be awesome. If I could rewind back to 18 or go visit myself in a time machine, I'd tell myself what the REAL scoop is on the Witnesses and what they believe. Then I'd tell myself that I should run as fast as I can away from that religion at all costs.
I don't know you Alan, but you knowing that you don't want to be in the Organization already puts you ahead of me when I was that age. I was already in business for myself at 18 but if I weren't and didn't have resources of my own saved, or inheritance put aside, etc ... I'd probably consider joing the military in some capacity to get my college paid for or maybe the Peace Corps to have a bit of a safety net under me for the basics of life - plus get some life experience and structure not related to the Organization. Otherwise, I believe the States of Texas and Alaska will pay for a person's ride for engineering school if you're willing to work for the State for "x" number of years. They even help you buy your house in the State, etc.
Are you still in High School where you could maybe talk to a guidance counselor about these programs or others and maybe confidentially about the challenge facing you? Do you have a job yet of any kind?
Timing is everything. Keep the timing on your terms. Prepare yourself. Save up money so you don't need to go back to family and ask for help. Prior to telling your family that it's your desire to leave the organization write it down in letter form explaining the reasons. Do the research so they can see it's well thought out and not just an emotional reaction to one specific thing. Have you read "Captives of a Concept" yet? Or "Crisis of Conscience"? Or "Combatting Cult Mind Control"? Those will help you if you haven't read them. I would personally start with "Captives of a Concept".
We'll be around if you need help. You're coming in to the prime of your life. I would love to have those years back that I wasted with the Organization. Be true to yourself. Follow your dreams. That's not to say you should rush into things. You'll find that what's important to you at 18 will be different by 21, then 25, then 30, and so on.
I hope you'll check in and keep us posted on your progress.