I am so confused. I would love to continue to try to help you but I feel like your responses are cryptic. What is it you want to accomplish? How does your brother fit into being a witness? A witness of what exactly? I’m not sure if your one post was referencing that your parents are supposed to cut off your sister- if that’s the case I can understand their stance. What happened to you should be hated, but that anger and hate should be driven towards the family friend who is the one who should be being charged.
I get the impression this is all incredibly hard to talk about @imdoneone ? Which might be why you're giving short answers or small bits of information. Looks like that is how you want to communicate. I think it is making it a little harder for me to respond and understand.
You're going through really tough things. Sounds like your siblings are all caught up in your trauma, either by doing the trauma to you or witnessing it. And then there is how your parents fit in. In terms of protecting you all (whether successful or not is going to be things you might be asking yourself or may in the future).
Do you want to say a bit more about what you want help with and how we can support you? Because I think there is this communication difficulty that is making it hard.
1) My mom knew and did nothing. Like I said dad was absent. He had his own trauma.
2) This family friend keep touching her and my brother said to leave her alone or he'll tell. He then began to hit my brother.
Well, they didn't. So how is wanting that helping you?
I'm sorry for what you've gone through, it sounds like an extremely rough situation. But I also know that seeking to retaliate against the person who abused you (your sister), or the person who did not help you (your mother), is not going to help you feel better. Instead, it may only distract you from working through your own pain, focusing on yourself.