Sweetheart, you sound like an amazing and extremely sensitive young lady, and I wish you every bracha and hatzlacha that Hashem will give you. Your issues are way beyond the scope of this CR, I think, so I am not sure what we can say that will help. You need to address these ptoblems with a rov whom you trust. If you had a kosher giyur at age one week, you still needed to officially re-affirm your commitment to Torah and Mitzvos when you became a BAs Mitzvah. It sounds like you have done exactly that.
I am not a Rov, so I cannot tell whether or not your siblings are considered Jewish born. I further cannot tell you the complexities of the law as pertains to children born of a Kohein and a woman whom it may be, by law, he is not supposed to marry to begin with.
Your questions are extremely pertinent and valid, and you DO need the answers, as they affect the course of your life. You have a lot going for you in terms of your own excellent analysis of your situation, and you sound mature beyond your years. there is a lot on your palte, and speaking to a sensitive Rov will help clear up soem of your concerns. I wish you all the best and a good Shabbos. You sound amazing. You deserve an amazing shidduch.