Tapping into my student pharmacist knowledge, I can say that Accutane is relativly safe for your liver. If your concerns are that much, just make sure you are seeing your doctor monthly for liver function tests. Your uncle's liver cancer shouldn't really put you at any more or less risk as far as I know. The big real concern for accutane is in girls because it causes major birth defects if she were to get pregnant. I don't think you have a problem here
So I say go for it, and clear up that acne.