Abuse and violence at home.

I live with my 84 year old mum, 22 year old niece and 18 year old nephew. My nephew is very sensitive, too sensitive and he explodes into anger over the smallest things. The other day, I forgot to close his bedroom door and he has this thing about mosquitoes getting in there. He started punching the wall over it. Last night was pretty bad. He drove his sister somewhere using her car and later went to pick her and a couple of friends up. Mum and I had gone to bed...1.30am, shouting voices came from downstairs. My nephew came into my room and locked the door and he started shouting some vulgar things to his sister. I was asking him to stop, but he was like someone possessed. I called for her to go to her room to let him calm down but she is as stubborn as he is, and wouldn't budge. Mum was crying, terrified in her room but I couldn't get to her, cause I was keeping them apart and trying to calm him down. I couldn't take anymore, I collapsed and started crying and hitting myself. My nephew suddenly realized and stopped and held me in a tight grip to stop me, took me to my room. I vaguely remember calling my sister, their mother, to come over, but not much after that, just bits. My nephew walking out of the house, then coming back, getting a basket of clothes and leaving again. My sister came and we all talked about it, decided that he needs professional help. He is one of the most honest, sensitive, goodhearted people I know, but I think he is easily hurt, has a bad view of himself, his pride is easily wounded and loses it, like someone going into a fugue state, he doesn't seem to have the ability to moderate anger. Everyone has gone into their separate corners today...but it's a sickening tense anxious quiet. I'm exhausted. I so wanted this Christmas to be a happy one cause we missed being together last year, but then, it's somehow a fitting end to a shitty 2018. Thanks for reading, just needed to vent.