my step dad hit my mom

Hi, its a long story but i would really really appreciate if read it until the end i had to vent and ask for help, Im sorry if there a grammar issues its not my firts language, and I'm not sure how this app works!

I'm the middle child of 3 siblings. Me 14 female, the oldest 15 female and the youngest 13 male, my mom has always been a single mom and I love and appreciate every single thing that she has done to take care of my siblings and I, she never had any of my dad's money and he has never done anything to try to take care of my or my siblings, I never seen a penny from him, I was raised by my grandfather's cause my mother worked all day to support us, even when she didn't had any money my siblings and I had always been in a private quite expensive school. I only remember 1 ex boyfriend of my, which didn't worked out, and my now step dad, I don't have words to describe how much I hate him, he has a lot of mental issues and he doesn't want to go to therapy cause he says it doesn't work and it's just a waist of money and time, (he has SEVER anger issues and OCD, at least to my knowledge) this issues make him always be angry with my mom, my siblings or me, cause if he sees that something in the house moved just less than an inch he would make a huge scene.

My step dad and my mom married In 2019 and had been dating a lot of years before that, but I never really met him until a few years before they got married, when we moved in whit him, they were always fighting, it didn't matter were they were they were always fighting, but for the most stupid things if I didn't said good morning to him, he will star an argument on how we don't want him near, that he pays for everything and just ask for a little bit of respect, that her family educated us like brats, and that he wanted a divorce blah blah blah, that were all of what they talked about in fights the worts was when they did it in the night time, I couldn't sleep with my mom crying to that guy yelling at her that her, her child's, and her family were all pieces of garbage, (my siblings and I are quite very clean, we keep things in order I always help my mom in whatever she needs and over all I help A LOT around the house, so do my siblings).

We live on a very small house for 5 people and 3 pets! And it's quite clean! But it's never enough for him, my mom never asked me or my siblings if we liked him, and I think she married him to have finally financial stability and she needed someone to help her with a lot of the expenses

I skipped a lot of very big issues and fights cause it was getting to long, but it got out of control! So let's cut to the chase.

I always suspected that he had hit her but I never knew, my mom never seem to have bruises or never showed any sing of it, she is a beautiful and hilarious woman she never failed to keep me calm or give my a smile so it was weird.

I heard the time when he hit her it was yesterday at 9 or 10 but the fight lasted about and hour, the silence of the night and the house always make their fights more easy for my to hear, so I heard it, it sounded like a slap in the face, but, I didn't do anything, I have always been scared of him with my life, I never raised my voice at him because I was afraid and know I don't know what to do, I can't do anything to help her, what can I? I'm just a 14 year old girl, what can I possibly do?? I'm planning on calling my grandma and tell her what happened last night hopping she can do some thing, and since I'm not in classes cause I'm on vacations I have to wait 2 weeks or less to hopefully get help from a teacher but know I'm all alone my siblings don't know that he hit her, I make this to ask for help and just needed to vent 3 or more years of suffering of my mom, my siblings and me. I want to talked to my mom about and I will do it if I have time alone with her. Thanks for reading this any advice will by super appreciated