School counselors eat this stuff up. Maybe not as much High School counselors, but sometimes them too. Certainly the college counselors want to try to help. Talk to your H.S. guidance counselor straight up about wanting to go to college with your obstacles- JW parents. Talk to your sister. Get your options. Try to earn scholarships, but even if you are at a point where it is time to leave High School, don't give up. You may find some ways to do this without your parents help.
In my opinion, you will have to confront your parents sooner or later about this. Especially if you are not baptized, be ready to say what you want to say- I WANT TO GO TO COLLEGE. I WANT A CAREER. If they don't support you in your decision, tell them you will have to do this without their support. Then go talk to a college counselor about how to do this. You may be able to live with your sister, or live at college if scholarships or counselors find a way to help you. You may need to go to a lesser college for a couple years and then try to transfer to your "good university."
As far as avoiding shunning from your parents, it is important to do what you can. If you are not baptized, and even if you are, you will probably have to keep the JW bashing to a minimum. (But I did like "Jecultah's Blindnesses.") Don't work so much on getting your parents out as much as you work on having the life you want. Then as time goes on, read things like Steve Hassan's books and try to apply methods slowly to helping your parents. The main thing would be to really let them know what you DO want, not so much what you DO NOT want, stick to your guns, let them know you will do what it takes and you hope to have their support or at least their presence in your life.