My 8 year old Step Son behaviour is unmanaged, selfish and aggressive.

[Beanybaby134]

Hi there,
I am really struggling with my SS behaviour and am looking for any advice. Apologies for the long post.
I have been in his life since he was a baby but only got in a relationship with his dad when he was 3. His mum left because she didn't know whether she wanted to marry or be a mum. She is now in his life 3 days a week.
His behaviour has always been difficult eg. Refusing to clean up after himself as it's your job, not listening when out and public walking off, screaming when he doesn't get something he wants in a shop, not following instructions basic instruction such as put in your jacket without arguing, sees everything in a negative eg. When we collect him from school and need to go to town he will sit into the car giving out it should have been done when he was in school, we just want to annoy him, tells us where he isn't going in town and what he wants while we are there.
None of this demands are ever meet and he is always asked to give a positive about his day and what makes him so upset.
He has hit other kids when they tried to take their turn of their own toys, he refusing food and making himself sick if you don't make the dinner he asks for, constantly acting like a victim if we are doing anything he doesn't want to ( doing the shopping, going for a walk), taking up to 4 hours a day to complete homework that should be 15mins max at least 2 days a week and can threaten you with violence in the process. He goes through aggressive patches with me and his dad eg, he threw himself on the couch the other day and landed on his brother, when his dad corrected him he ran to kick him twice.
We have tried gentle parenting, reward charts, time out, natural consequences, love bombing and 2 years of play therapy but nothing is working and now the he is behaving badly in school ( he used to love school). He now has a step brother of 5 months who he sees no competition with due to the age gap and interacts with frequently and includes when demanding to do activities. (Which I am very happy about)
His behaviour has always been difficult but I'm the last 2 years it has gotten worse, he can be a sweet child and has lots of friends but these moments are generally when he is doing what he wants.
I feel like we have tried everything besides psychological assessment which his mum refuses to consent to (we are in court seeking assessment and custody change)
Has anybody experienced this ?

To clarify he has always lived with his dad and his dad has always been his full time parent. It was his mum who left his life for a period of time. I have always been in his life as we are all in the same friend group. I didn't become his step parent until he was 3.

So you need to turn to your partner and his parenting over the past few years that has resulted in this poor child behaving like this

He has been with us his entire life. The situation has been very complicated and he has definitely been but in situations that no child should have. Nobody is a perfect parent but we have done counseling as a family and individually with parenting strategies. We have worked closely with his play therapist and we love on him and give him every opportunity. We continue to fight to protect him more but not everything is in our control. When in mums his boundaries are very different, a lot of her family members are active drug users which he is aware of, he has seen aggression situations and handover now take place in a public place at our request so he feels safe in his home, he is allowed play violent games like GTA at his mums and not allowed here, he has unlimited access to electronics and being unsupervised on the roads. He is not allowed in our house, this also makes him very upset. We are fighting a losing battle at the moment and his two houses are night and day. He has gone through so much at a young age but we are out of options until the court appointment psychologist report is complete. (This is our third time in court to put boundaries in place for SS security)

Given all you have tried
and fact of his mother’s poor existence with the drugs and gaming etc
there isn’t much more you can do except support your husband and ensure your son is safe

His mother has almost 50/50?

I’d be gathering evidence of her poor situation and then go to court again
you need evidence

Can I ask if yous think it's down to his mum that he's acting the way he is, I'm in the same position with DGS