I agree with the positive method totally. He need some time first to adjust to his surroundings. I would just sit on the floor near him, maybe with some really smelly tasty meat and just sit and gradually see if he will hand feed, may take quite a bit of time. He needs to develop a trust in you before he can move on to anything else, and come to you totally willingly. I would keep the other dogs away totally for now. I would take him out to pee though he can't hold it forever, preferably with no animals or people around. Just my 2c, I am just thinking of what I would try.
Started Primal June 2012 at 148.5lbs, and 5' 1", reached goal weight in 5 months.
Lowest weight 93lbs - too thin. Now stable at around 100lbs much better weight for me at my age.
Primal, minus eggs, dairy and a myriad of other allergens.