I need advice

This is my first time ever on here so I'm pretty nervous, and honestly I'm pretty scared to even type this out. I need some advice from people with more life experience than me (this will be a very long read I think) but back in 2019 my dad was arrested (its some really bad stuff I don't want to get into yet on this app) but fast forward to 2023 my mom met this guy called "s" he was a cool guy and he made money. Which is what we desperately needed as me, my mom "M", and younger brother "G" were constantly on the brink of homelessness and could barely pay bills. His 2 kids "J" who is 7 now (very important) and "C" who is a year younger than me, S was dating my mom for about a year and then ghosted her out of the blue. It was a lifesaver for me and my brother because J and C were some of the worst behaved people I've EVER known. About a year later though just before summer 24 they got back together and after the summer I had to move in with S and his kids, I switched to a much bigger school in a much bigger town. Life was rough last year as I was getting bullied a lot and I wasn't an upperclassmen yet (I'm going into jr year now) i had a lot of stress on my plate with school and this new school didn't offer the same extracurriculars that I loved at my old school. But I'm really getting off track so back to what I need advice for - C and J have been out of control since S doesn't like to punish them and rarely even confronts them about their actions, it seems me and my mom have become personal slaves and i constantly have to pick up after J and C, now C is extremely manipulative to his whole family and its constantly telling his family lies about me, M, and G, even though he's younger than me he bullies me relentlessly because if I even look at him the wrong way he tells his dad some crazy lie about what I did to him, I can't take it anymore after a year of this constantly, it has gotten worse withing the last 4 months since C has been making J tell lies to his dad and constantly making stuff up about me and MY family, his dad can't handle them and I can't keep getting bullied, if I stand up to C his dad will definitely break up with my mom and we'll be broke again with nowhere to go, but the lies and bullying are so bad you don't even understand. I don't know what to do because I CAN'T keep living like this (its bad enough were ive considered ykw almost daily and self harmed to keep myself from snapping on c and ruining everything), but I cant go back to being broke, my mom is constantly trying to help me but there's nothing she can do and she really loves S. I just need advice on what to do because I don't think I can keep doing this. (I'm not gonna get into the bullying he's done right now but it's terrible)