Step dad- is this right?

I just turn 15. My mom & him r marry & i knw him since i was 6. He treats my family wrong. This might get personal but i hate seeing my mom cry becos of him. He ruins our family.He can be cool but most of the time he is a dick & my mom agrees. I ask her why she doesnt leave & she says its because of my brothers and I. I have 3 brothers but i am the oldest another is 11,4, & 5 months. My 4 yr old and 5 month year old bro are his kids but me and my 11 yr old bro are step brothers we have different dads. My real dad lives in a diff state with my other bro who is 13.My step dad treats me and my 11 yr old bro like slaves. He would never get his *** off the sofa. My bro and I dont respect him were afriad of him. Were afriad of him because he use to abuse us. I dont have much memory but i no he did. I think i was about 8 when he started to hit me and my 11 yr old bro. He always use to hit us when we do stupid stuff or annoy him. I have a memory and i member it perfect becos it was really the worse. It was about 4 yrs ago & we were home with him. My mom was working she always does to pay the house and he dnt becos he cant find a job becos of his record of his past. But back 2 the day it was noon & he was sober taking care of my bro who was about a year old & was in his room & we wanted to ask him if we could play xbox but my brother and i were always use 2 like fight but not loud becos were afriad 2 ask. Then i finally went up to ask his door was close and when i knock he came out & started to hit me and kick me and slam me againist walls yelling dont you know your brother is asleep & i didnt but now he doesnt hit us as much because of my mom but he always home. He always yells and scream at us. We got to do everything 4 him like get his shoes & turn off the light even when were downstairs and hes up. He says he cares but im starting to think tht he doent we feed ourselves. I have a memory prob & i think its cos of him. He hits me on my head & i get bumps. Wat shuld i do?