Hmmm sounds very much like what my younger brother went through at that age. He was being bullied though, sometimes there is a reason behind it, sometimes not. All I know is that it's very hard to reason with them when they are going through that phase. I'm 10 yrs older and I could not talk to my brother, he would bite my head off. He was able to talk to mum about how he was feeling and why etc. Is there someone he can hang out with who is older, that would be a good influence on him, could suss him out etc? Can he chat to you about things? Maybe he needs some mum time away from his sisters. It does pass My brother is now 18 and a lovely boy, gentle, caring and very happy. Everything you've instilled in him is there and you'll see it when the hormones calm down a bit or when he sorts out whatever it is that's worrying him. Maybe nothing is going on and he's just being a moody teenager. Good luck & have hope, it gets better