Please ignore the people that have no idea what it's like to be in a situation like this. They merely don't understand, rather than anything else.
Also, if this were about the OP's DH, everyone would be shouting LTB and encouraging you to call Womens Aid!!
You are getting this behaviour as he's trying to tell you something. Is there any way you could get him assessed by someone (preferably a Behavioural specialist)? You hate his behaviour, not him - or you wouldn't be on here at the end of your tether.
You also have a duty to keep your other children safe and you need to point out to everyone that you cannot take anymore.
You are being a responsible parent by asking for immediate family intervention, for the crisis point you have reached.
I haven't had it to the extreme that you're experiencing, but there are lots of us who understand and sympathise with you. My DC's 'behaviour' was due to an underlying condition, that I'd spoke to the Paediatrician about when they were first 4, and I had been fobbed off!