My (22M) cousin(16M) has become rogue and rebellious and nearly broke my aunt's finger.

So me and my family live in my aunt's (sagi mausi) house on the first floor and they live on the ground floor. My uncle is in army so he mostly remains far from home. My aunt has one boy and one girl child, both younger than me. Everything was fine until my cousin (aunt's son) got in class 9. After getting in class 9th he started to have company with instagram badmosh type boys of his class. As the time passed he became one of the boys who says- "Are hum toh jaat hai", " jaat dil nahi haddi todte hain". I think it's enough, you can understand now. Also, his thoughts about women and society has also become flawed. Always talking to friends on Instagram, watching reels, going to school with a shawl (He thought it was cool), Idealizing Rajat dalal, shouting on mother and abusing her (not gaali but still abusing like aapke paas dimaag nahi hai like), hanging out with friends all the time. Then he slowly became violent and aggressive with time and used to throw hands on her mom ( not hitting but throwing her away ). Now listen what happened today. I was chilling with my headphones on my ear. Suddenly my mom came and said- "behra hai kya niche ladai ho gayi chal mere saath aur sulah karwa". When I went there my aunt was insisting to give my cousin money to go to swimming pool with friends which he refused to take because just a few minutes ago she refused to give him money because he had already gone there just a few days ago. Then he got angry and said he won't take even if she give him thousands of rupees and also tried to lock himself in a room. When we all were trying to make him calm and not letting him alone in room ( my aunt was scared that he might do something ), so she tried to stop the gate with her hands but he was so enraged and furious that he didn't see her hand and tried to close the door with full force resulting in badly injured little finger of my aunt. She started crying, blood was coming like fountain. We did something that we could do then I took her to the nearest hospital. Luckily the injury wasn't that critical. But his behaviour is becoming gruesome and violent. I don't know what steps we can take to get back him to his previous form. Please provide your advices.🙏🏻

TL,DR- My cousin has become rebellious and almost broke my aunt's finger in his anger.