Make a plan this week to start fresh.
Set aside some time to spend with him(even if it's hard at tje moment).
Praise the good things he does especially in regards to his sisters. Really big up when he's gentle,kind,quiet etc. "I love how gentle you were with the baby". Give him small rewards either by spending a few minutes with him or a nice snack.
Have a NOW and NEXT board.
A visual time table of his day and activities that he can have some input over.
Buy some feelings books (sad,angry,lonely,happy,jealous etc)and read them with him over and over again.Talk about them after , ask if he ever feels like that.
See if you can make him a calm corner(with cushions,sensory stuff like liquid timers,tangle teasers etc), not for punishment but so that he can go there and calm down,sort out his emotions .
Make a list of house rules, keep it basic and simple. Let him have a say.
If you can spare the time have a daily or weekly notebook for him with what has gone well, what could've been better, how could we fix the could've been better.
Give him responsibility with tasks that are reasonable and safe for hom to do. Make him your helper.
Have a feelings board near the door so when he comes in he can put a peg for example on how he's feeling that day- happy,sad,angry
Ideally you'd get professional support right now,but until then you will have to keep trying.
I know it seems like an overwhelming and daunting task list but these are just some ideas, pick what is doable/you think it will work. The idea is to stick with it, be consistent, firm but loving and fair.
Some days will still be shit, but the goal is to have less shit days and hopefully to manage to break this cycle of anger and resentment you are both stuck in.