A.B.
You didn't mention Dad...is here there? In my own experience, before my separation/divorce, it was my eldest son & myself that worked together, always (Dad was relatively useless as far as being around/involved and/or helping). He is THE most responsible of all 3 of my children, to this day at age 24. I helped to do that to him, I helped create this because of how it is I related to him. Therefore, I had to work at undoing it, after the split & still today.
So, my question to you is how is it that you relate to your son? There's a saying that goes, "when you point a finger at someone, you have 3 fingers pointing back at yourself." In other words, before looking at your son, take a look at your own behaviors because if we want to try & change someone's behavior, we must first look to ourselves & our own behaviors. It's no wonder my son fought with my other 2, like he was the boss.......I basically gave him the status of the father, so I had to constantly step in & say, "I'm the mom, you be the big brother!"....constantly...
I would acknowledge his age/knowledge/status in the family. Praise him for who & what he is. Give him the due that he deserves because it sounds like he's literally fighting for it.....does this make sense..? As in, "you're so very mature for your age", "I so appreciate your help", "I know it's difficult for you..", etc....after these words/msg's, tell him what you expect from him. If we give what is being looked for, people don't have to fight for it. Help to GUIDE him into acceptable behaviors. Accept ONLY age appropriate behaviors (& yes, his fighting, to a certain extent, IS what he's suppose to do in order to separate & be different) LET him BE the kid. It has worked & is STILL working with my eldest son. A little bit of praise goes a long way! :-) I wouldn't fight the tide but rather go with in order to help the situation & all involved. I hope this all made sense....good luck!