Find more dirt about him. Find something that would shaken him too. Let the game be played fair and square. Or maybe compromise things with him. Find peace with him. I used to fight with my brother too. But I've learned to ignore him. No I completely make him feel like he doesn't exist in my circle. So that's how I stop fighting.
I have an irritating, manipulative, liar brother who is so selfish and each time my parents either ignore our fights or we both get scolded (mainly me). The best solution is try to ignore him and don't poke into his business AT ALL. At the same time be very secretive abt yours. Do not let him think he has all the power. Collect more blackmail Material if you can and make work with the own that you have. The key is to not let him see that he is getting under your skin.
I am in the same situation back then.. My parents are religeous that's why they are uptight about me being fujoshi and when they learn that I read BL they lashed out on me but I stood my ground and tell them that it is my hobby.... As for my brother which also annoy me, i remember that my fist is better that my mouth that's why there is one time we got into huge physical fight and i didnt stop not until i see his bloody nose though i also suffered one hehe!!
I have a younger brother and we're constantly fighting. We're never on good terms and when we are, it doesn't last long. He had found out about a year ago that I like BL and I read it/watch it. Well, he is the type to snitch, but he doesn't because I had something even more incriminating about him. Well, now that that trump card is gone, I know he's going to spill it at some point. Just as an FYI, my parents are huge homophobes and wouldn't even tolerate me talking about lgbtq people in my house. So if this is found out, I'm fucking doomed. My brother doesn't know how to keep his mouth shut either, so when he's mad, he mutters things under breath like "at least I don't read about boys kissing" or something like that and it seriously pisses me off. The only good thing I have going for me is the fact that my parents don't like to interfere with my brother and they don't like to snoop into what we're usually fighting about. They just don't care, and they know that me and my brother fight a lot so they've learned to ignore it. But I feel like soon enough, they'll hear my brother while he's saying one of his comments and be onto me. We've lately been in a huge fight and I think he's going to let it out soon. I don't know what to do to stop this before I'm found out.
Offer me your advice fellow fujodanshis