Ha!! I got enough to worry about without having to put up with a 27 year old kid.
OK, first thing....rules. Your house and everybodies house has rules. He hleps out or gets out. He respects everyone and always remembers he's a guest. Don't let him forget that.
Next....He WILL do rehab and straighten his physical self out. It helps a ton with the mental self. If he don't wanna do it then he goes. Rules. Remember?
Don't worry about his sorry ass whining. Drink your beer in front of him and refuse to let him have one. He don't like it he's out. Your house. Your rules.
Third....He gets a job. Period. He pays rent or he's out.
In fact, I'd put him in the shed or the barn with no TV.
But that's me.
In fact, if you make his life there just short of miserable he'll eventually leave on his own. Rehab, no booze, no TV, go to work, put him on a diet, PT his ass if you can pull that off (digging post holes works or cleaning out the barn). Hell, most of us would get out of there the first chance we had.