Brother(11M) once beat Sister(24F) and now she lives separately.

So this post is not about me. I am posting instead of someone else.

Brother(11M) is not directly related to our family. He is the son of our Maternal uncle who is too sick to take care of his child, both emotionally and financially. So he lives with us. He loves n respect all of us. His mother is Autistic or something( it's not clear) so Our uncle started his counselling from early age. All therapists gave diagnosis of ADHD and some medicines to control the symptoms. Ever since he was a baby, he lived ethi us only. Sometimes he says stuff like we're his real family and not his mother. He is now going to be 12years old. Sometimes he does what a child does, lots of mischief and he gets scold for that. But he never reacts in a negative way. He always listens to us.

Yesterday we were sitting in an AC room and he was playing some kind of game. He switched off the fan. My mother came and sat beside us demanding the phone back as it was time for him to study. He refused and my mother started scolding him. She also switched on the fan. My brother got up and switched off the fan and refused to give the phone . My mother started scolding him again, as she just came back from kitchen and its too hot. My mother then instructed me to snatch the phone. I proceeded to do that . In a second, his eyes turned all red and started to beat me. He told me not to touch him again or he'll personally see to it. He also threatened me saying he'll break my hand. I was sitting there dumbstruck by it all. I never saw my baby brother, for whom I used to change diaper, like this.I got angry and proceed to yell at him and give him a spank. He pounced on me, breaking my clutcher, elbowed me on stomach and tearing my tshirt. He also beat me in ears where I got new piercings. My mother barely managed him off him and started yelling at him. I started crying and left that room. In the evening, my Uncle got and started making me understand to forgive my brother as there's always a genetic component. His mother was also like that with me and my mother. I always protected him from his mother and now I'm seeing the same avatar in him. He is now staying at my grandparents house.i told my mother not to let him in for today as I am still not okay with what happened. Everybody is trying to make me understand that he's a baby still and that's why he is going to counseling. Today I mentioned that my head is still hurting and cannot think straight. My mother suddenly changee her mind and said my brother is coming back this night only. I said no and she reminded me that ," bhai beheno m Aisa jhagra hota h, koi badi bat nhi h, tum khud Apne bhai beheno k sath bht ladti thi". I asked her If she sees all siblings quareling and this incident the same way, she said yes. I was in awe. I feel so hopeless and my heart is broken. I cannot go through what I went through his mother in the past. I thought I was raising a good child but yesterday's incident told me he doesn't even respect me enough in that way. I am planning to shift in with my friends ( lives 30km away) who stays in flat due to job. But I am again thinking if this move will have negative repercussions? I am trying to protect Myself. This outbursts will happen again in future, I am sure of it. My mother is against all of this. She's asking if all these years of love is out the window because of this incident. Again, it's all true that we're the family of my brother. He doesn't have anyone else to take care of. I don't know what to do?

Any mature sensible opinion is welcome.

Edit: please refrain from saying that you guys used to hit your siblings . This relationship is not of some siblings but of a guardian. Age wide difference is what makes the OP confused.