I need help someone tell me what to do?

im 11 years old and i have a 6 year old sister. my parents had me wen they were 16. i am absolutley terrified for my mother. my parents have a abusive relationship. one day my parents started to argue and i dont know what made that happen so my dad got so pissed and he broke my moms new laptop and **** went down, fist went flying. i was teriffied. my dog went in to hidding in my parnts closet an i also locked my sister in my room i went in my room with the door open incase i had to help her. i heard my mom screaming so i ran to her room through the messy now broken living room and saw my dad punch her. i screamed dont you dare hit my mother again. then he looked at me like i was some type of disease (note:my mother is a very strong independent women but she just caved because she was under a lot of stress.) he ran up to me and punched me in the face and my head bounced back against the wall and i fell on my side. he walked up to me MOM i screamed then he kicked me my mom slapped him my mom said go to your room so he wont hit you. i made it to my room and leaned against my door and had a break down. 5 minutes later i head a knock at my door who is it i had stuttered me and gia my mom answered i let her in. my mom held me and i clutched back on to her. my mom kicked him out that same night. a few nights later i fell asleep in the living room and woke up to him there walking around. my eyes were wide bye then and i just walked away, aparently my mom let him back in. to this day all three of us me my mom and my sis suffer physical and verbal abuse from this nasty person. even wen i was little i stuck uip for my mom. when i was 5 they got into a fight and i bit him as hard as i possibly could to get himm off of her i then called 911.i dont know waht to do now im scared. my mom might be staying with him because we are currentlt on Wic and she is pregnat......btw this was b4 she was pregnat. he calls me a fat all the time altho im not and he knows i am very emotional and self contious. he calls me and my sister dummys for absolutely no reason and he knows my sister has learning problems she is in 1st grade.he is aparently on workers comp because he hurt his arm but hes perfectly fine now cuz he goes to play bball with his friends and the doctor told him he was able to report back to work but he doesnt he hurt his arm in february. he also is not a man of his word we have to beg him to fix something like me and my sisters beds. i need help id know what to do im not trolling this is serious. any rude answers will be reported.