He needs tough love OP, or not tough love because you must be sick to your teeth of him.
I firmly believe no one person gets to rule the house.
Pack his bags and get him out of the house.
Call the policebif he decides to cause a scene.
He is over 18 and has no entitlement to your home.
Your poor children witnessing such drama.
Do it now when the shock.might get him to cop on, otherwise you could have 5+ more years of this.
Tell him you are done.
He needs to move on as he clearly isn't happy in his home.
Reclaim the bedroom so that he never can return to that room.
He needs a dose of reality.
Unfortunately in life we often get the amount of shit that we will put up with.
Say No more, and mean it.
You sound like a great mum, but he needs a dose of real life, fast.