Not to judge, Jynx. But from what you say, it sounds like you're dealing with a one-track mind kind of thing: synonymous with stubborn and bigoted. I live with a pair of people like that, and I can understand how horribly frustrating it is. I don't know the extent of what you are dealing with in such a regard, but here's what I did.
I left them out of it. I really don't care what they thought, and as much as I wanted them to accept it, they would never be swayed from what they believed what it was. As nice as it is to have people know and understand your interests, there are just some people who are going to try and hammer you down; they will try to make you into what they see you as. You can kick and scream, give all these justifiable points and reasons, but ultimately, they won't care.
Yes, I know it's hard to accept. But stubborn people just won't budge, plain and simple. They don't want to, they don't think they should, can or will change in regards to opinion. Your best bet would be to go into a therapy/counseling session with your family and explain it to the therapist/counselor. If that does happen, remember to explain your story and your views first, what you believe in, avoiding touching on the rather questionable areas of the fandom until it is brought up. "There might be some people like that, but I mean it when I say I'm not one of those people!" Things like that. You should really rehearse what you're going to say, and play it out in some way so that you aren't interrupted and/or distracted, because I know how that can make things difficult.
I'm not saying keep it a secret, but I am saying that you should not allow their misguided opinions send you astray personally. You know who you are, and no matter how closely related they may be, they do not. They see what's on the outside, but they can only be left to assume what's on the inside - and we all know what assuming does.
You just need to step back, relax, and concoct something within reason of your family. I would say ask this: "What can I do to make you see I'm not what you think?" The answer you receive should be a decent explanation of what you're dealing with. If they retort with something like, "just stop doing it," then you know it's out of your hands or it will be extremely stressful to just point it out to them and get reason across on your own. I know a lot of parents act like just because you are young means you know nothing or are completely oblivious to reality, and it is a rather immature mindset in its own right, and again, I deal with that on a daily basis. But if they answer in the manner of "well, get me some legitimate research or come up with an intelligent reason," then you have a good opening. Do your research, give reliable sources, and explain in the most level headed and mature manner that you can muster. Most counselors will back you up after an explanation, and a professional opinion will certainly sink in best.
Again, I don't know your situation, Jynx, but just be liberal with the detail and information and keep a level head. Organize your facts, your reasons, your own beliefs and the beliefs of others who assume the same denomination. It's just like writing a persuasive essay in English class. Be concise, precise and above all, honest.
Hope this helps. Even just a little.