I need to make this really important decision and I don't know what to do. Help

Okay, so about three weeks ago I went to my dad's house for the first time in 9 months. So, it's like really bad there; he's very abusive. Physically and verbally. I live with my mom and I used to go see my dad every other weekend. I never liked going there. It's just so horrible; seeing my siblings being beat and my dad and step-mom constantly fighting.

My dad has never hit me or called me names, though when him and my step mom would fight she would call me a bitch while my dad would call my step brother a bastard. This was ongoing since I can remember which I guess would be when I was about 5, but I'm sure it went on before that, too.

Anyway, a couple of years ago my sister and I ran away. We went to the cops and both told our stories. I told them everything I knew from the years of going there every other weekend. My step-sister, though, did not. I guess she was scared of what might happen if my dad found out. I don't really blame her. So, the cops were supposed to look into the abusiveness and all. This would be the second time CPS (child protective services) was called on my father. The thing was they never followed through.

So, like I was saying before I went to my dad's house and my sister and little brother just told me some really disturbing things. How my older brother is not allowed to see me, how the my step-mom was cheating on my dad, how my dad says he only loves me and my little brother cause we are his real kids, how the window in the kitchen broke during one of their fights, and the list goes on continuously getting worse and worse. Also CPS never followed through because apparently my dad somehow knows one of the cops who my sister and I went to, so the police are covering for him.

Now my little brother was also contributing to this conversation my sister and I were having. Which is not normal; he usually tells me everything is great there. He says I need to come over more. He tells my dad what my sister and I are saying; not this time though. If my 8 year old brother is admitting that there is a big problem than there is a big problem.

Anyway, what do I do? Do I report this? Will anything come of it if I do? Will it make things worse for my siblings? I am so confused. I do not know what to do. I've talked to my friends, family, and counselor, yet I still haven't found the answer I'm looking for. I just don't want to do the wrong thing. If I don't report this what if something really bad happens. If I do what if my dad beats them more. If anybody would like to share their opinions please do. I need help. This decision is really important and I'd like to know what other people think.