Transphobic brother ?

For years, like ever since I realized I was a guy, my little siblings (not counting the one that was just born) have been calling me and my older brother he/him and using masculine terms for us, because we asked them to, and they just immediately switched, it was fine. They started calling me my name, too. The rest of my family is very transphobic, but they stopped correcting them years ago.

And then recently (in the last few months) my little brother has suddenly been misgendering us. It's got to the point where genuinely I can't remember a single time in the last month where he got my pronouns right. It started with "edgy" comments (for ex. he'd come up to me and my little sister talking and be like "what are you girls talking about?" or when we were playing badminton if I was the only boy on a team he'd insist it was a girls team.) and he always laughs and smiles when he does it, like he thinks it's cool. Everytime he does, one of my family members jumps in like "it was an accident, he's just used to it, you can't expect him to get it everytime" but again he's known I'm a guy for YEARS. 

My older brother has the theory that Taylor (my dad's girlfriend) is telling him to. Which I don't doubt, because one time I heard her and my little siblings talking in the kitchen, and my little brother called me she, my little sister corrected him, and Taylor immediately screamed "It's fine!"

My little brother has also just been being randomly rude to me, like everytime I say something, he disagrees in a very "I'm better than you" sort of way? I don't know how to explain it, it's like he smiles and just insists he's right. It's very reminiscent of the way my dad argues, like he's silently saying that you're an idiot.

In the same time frame, my dad and his girlfriend have started calling me and my older brother he/him and using our names, but only when speaking directly to us or where they know we can hear. And like it's just very obvious to me that they're only doing it because I want absolutely nothing to do with them and think this will get them brownie points. The biggest proof of this is that when I piss my dad off he immediately drops the act and starts misgendering us again.

I don't really have a point to saying this, I'm just really frustrated.