Child with I think PDA in a largish Family - HELP

So in a nutshell my little boy is 8, he has never really liked being away from me, when he was 2 he only went to playgroup 2/3 times a week, he has one older and 2 younger siblings. 

When he was just 4 we went through a massive family trauma, he lost contact with his siblings and went from appearing NT to having violent, aggressive meltdown anywhere up to 8-10 hours a day.

I sought professional support but we were turned down at every avenue - I tried the GP, Social Services (who should have been supporting us anyway but refused).

At the same time he started school - and he HATED it, he would strip his clothes, take his seat belt off, try to climb out of the car, anything that stopped me taking him.

He would then be fine in school and start again when he came home.

He also started being violent to his siblings and I am ashamed to say I lost my temper and really, really yelled at him a few times.

Fast forward a bit and we moved house, I gave up work, his tantrums and melt downs and outbursts eased, but they continued.

He was OK in his new school but he never really liked it - he was slow to read and even slower to write. Then at nearly 7 he literally could read, over night - he suddenly could read everything put in front of him. His writing though remained slow, he could write, but he never really wanted to.

Eventually I managed to get him some play therapy (after he bit his sister so badly he nearly took her eye out) and we saw massive improvements. After the first session the play therapist asked if I thought he was autistic.

Real problems started though when he went into Year 3 - I knew he was resitant to change and would struggle so I put together a plan with the SENCO (he has no diagnosis school has persitently told me more or less it is all in my head although he had an IEP).

Within 3 days of going into year 3, (same school different building and now "primary not infants"), he started wetting the bed and having meltdowns daily as soon as he walked in the door.

After 2 weeks I contacted the school, found out he was being kept in up to 3 times a day as his writing was too slow - I told them to stop and thought that was the end of it - however the behaviours continued and he started wetting in school as well. School kept insisting he was fine in school and him telling us he wasn't being allowed to go to the toilet was him lying.

By now his genitals were sore from the constant wetness.

At week 5, we went to parents evening where we discovered he was still being kept in - requests to the head master to put a stop to keeping him in (bearing in mind they were also aware of the early trauma) were ignored and we were told the head would "support Mr X in whatever methods of discipline he chose to use".

This eventually led to a day of school refusal. The next day he went in and they kept him in at breaktime, AGAIN - so we deregistered him from school.

That was around 16 months ago.

It is very difficult to get him to do anything he doesn't want to do, he is easily distracted and prone to meltdowns if pushed.

He categorically refuses to write (I believe he is phobic) and I have removed all electronic gadgetary from the house or "lost" the chargers, because he is impossible if he has had more than an hour of screen time.

Despite this home education went well, he loves documentaries and reading, so it has been easy to provide him with educational materials that may not suit mainstream school but have suited him - however he is beginning to be resistant to this form of learning as well now.

He is very lacking in boundaries - he is incredibly rough with his siblings, he overwhelms them with love - no amount of telling, talking or explaining stops him cuddling them, picking them up - or when he is in a mood lashing out at them.

Today (this is the second time in 3 weeks this has happened) he upped the ante, he punched his sister, stamped on her, and then put his hand over her mouth so she couldn't call out for me. This was out of the blue because she asked for some alone time. 

When I  sent him to his room to calm down he started screaming and swearing at me - he fucking hates me, I am lower than a piece of fucking ***, I could *** the *** off and plenty more. And then trashed his bed in a systematic manner.

This went on for an hour, with his 2 younger siblings listening although I took them to a different room.

Eventually I pushed him out of the house into the rain and kept him out there for 5 minutes upon which he calmed down (he always does with this but I am sure there must be better methods).

This is a non swearing house and this is not behaviour he has seen from anyone he comes across and he rarely goes anywhere without me).

Getting him out of the house is a struggle and he absorbs all my energies - plus I feel like I am failing him, he isn't in school, he is resistant to anything he does not want to do.

He is really high functioning and very sociable and I don't think we will ever get him a diagnosis, but he struggles to function in a main stream world.

I really am at a loss as to what to do - but as he is getting older I am getting worried he is going to hurt one of his siblings - or sooner or later me. Sometimes he is so violent all I can do is restrain him until he calms down - he wont allow walking away all the time, depending on his meltdown this just leads to him following and attacking.

Anyone got any ideas?