* H*is understanding and communication is very poor which makes it really difficult.
^^ this.
Behaviour is communication.
Communication/understanding difficulties can and do impact on behaviour.
You need to look at working on improving lines of communication between you to aid the improvement in behaviour.
Don't try and tackle everything at once.
I'd start by looking at a couple of behaviours at a time, and thinking about what could be causing/triggering them, and either remove or reduce the trigger.
I'd also focus on communication, are PECs or a visual schedule something that you've looked at?
Also pre-warning of changes. (Count down to the change, eg In 30mins we will be packing away, in 15mins.. 10.. 5..2..),
Maybe also look at controlled choices. (If understanding of speech isn't there you can always use pictures to choose between 2 things)
These can help dc to feel in control (even if they're actually not.)
For us choices are one of three things; negotiable, flexible nonnegotiable or nonnegotiable.
Eg,
tea is negotiable, at controlled choice of 2 things is given, chicken nuggets or fishfingers, peas or beans.
Nonnegotiable is what needs to happen now. No choice. I don't have many in this category, School, and holding a hand to cross the road.
Flexible nonnegotiable is something that needs to happen, but a choice over when/how is given. Which are you going to do 1st wash your face or brush your teeth. (Either way they still need to be done, but an element of choice is given).