As torn as you are, and as torn as you will be, he must leave. Although you say he was disrespectful in high school and that's nothing major, it was, and is major. Since then it's all been downhill you say - well from now too, it'll all be downhill.
It will continue to be downhill, the violence will increase, the abuse of you three will increase, it will all get worse unless he faces the consequences of what he does, and is removed from the home that he abuses, the money supply he steals from, the sister who he bullies and scares, and the parents who he has no respect for and physically attacks.
Please, I implore you, give him a date within the next few days when he has to return to get his possessions. Tell him his room will be cleared out, anything left will be binned, but he is on his own.
Please also remember, this is not a child. This is a 19 year old young man. Old enough to father, to vote, to join the army, to get a mortgage. Old enough to be totally responsible for his behaviour, old enough to treat you all with respect, and old enough to cope with the results of his choices.