What should I do about my crazy brother and dysfunctional family unit?

I'd like to think I'm the level headed one in this family. I live with my mom and dad, two younger brothers, and younger sister. We are as dysfunctional as they come. My brother who is 20 years old snapped in the car and didn't think anyone would say anything. I, the eldest brother- 22 years of age, called him out on it and told him to calm down. He said to my youngest brother, 12 years old, "**** you." That's not right at all, no matter what the youngest brother did or said, it's not right. I told him to calm down and watch his mouth and he started mouthing off to me. As soon as we got home he started threatening to "beat my ***" in front of the whole family and I asked him, "is that so?" I suppose he got bent out of shape because someone questioned him and his ego was in jeopardy. I don't know. Anyways, he started pushing me and I did nothing back to him. We went into the house and I told him to fix his attitude and he started going crazy again. He ran up to me, tried to choke me, and I still did nothing. I don't believe in physical violence especially towards your own family. I went to my room, calmed down, and he came knocking at my door asking if there was something wrong with the internet. I lied, said no, and shooed him away, but his attitude and actions earlier were still bugging me so I gave him a piece of my mind. I asked him, "How can you come up here and ask me so kindly if something was wrong, did you expect me to fix it." As his face was in disbelief, I continued to lecture him on how much bullshit I thought the situation was so he decided to run into my room, tackle me on my bed, and gave me a series of punches to the head. Though it didn't hurt or leave me with any scars or bruises, I feel like this is not normal and should be settled or addressed by someone else, because obviously my words don't reach him. My parents won't do anything(as a matter of fact they just got into a fight themselves, my dad picked up their bed and put it in the hallway and i ume he drove off to go drink somewhere) and I think this is an extremely horrible environment for my younger brother and my little sister. What should I do? What can I do?