WOW, big surprise! He treats his own parents like crap and you think its his parents fault and let him move in? Being a mother yourself with a son you honestly thought that it was all this ungrateful jerks parents fault that he was kicked out? You REALLY thought that this jerk would treat you better than his OWN mother?
The 4th commandment is
"HONOR thy father and thy mother: that thy days may be long upon the land which the Lord that God giveth thee:"
The bible says that unruly kids are to be brought before the elders and stoned to death, this is why the commandment gives this promise, if you don't honor your parents your going to be judged by society who is going to stone you because God knew that unruly and non honoring children end up to be worthless scum on society. . Maybe we should get back to biblical teachings instead of this garbage called 'tolerance' !!
BTW, the other commandment is "Thou shalt not kill". Interesting that its listed after honoring your parents! So no, you can't kill him.
Personally, I would have your husband move out there and sleep there. In just a few days he will be gone.