Pack his bags for him, change the locks, and drive him to a homeless shelter and drop him off.
AND DON'T LET HIM BACK IN!
He is disrepecting you as he did his parents because he can get away with it. You shouldn't put up with that.
Feed the fish to the reptliles...that takes care of part of the pet problem (okay..just kidding there).
I know this is all easier said than done. My mon is in a similiar situation with one of my brothers. She is moving out of state soon to take care of her parents. My brother is supposed to pay rent on the aparment, (she owns the duplex, upstairs is one of my brothers and his family, and downstairs will just be my younger brother). The problem is that 75% of the time my brother doesn't have a job. I think he may have one now..it changes every other month. My mom has been delaying her move because of him and my youngest sister...but since the sister is going to live with me, she only has to worry about him. She told him she is going this fall, come hell or high water...and he better pay up on the rent.
I dunno how it will all work out.
Let us know how you make out...maybe he will shape up if you have another talk with him, but I doubt it.