You begin with baby steps. Expect nothing. Set him up to always do the right thing by keeping him on a leash next to you, even inside the home. I do this with adult foster dogs, sometimes for several weeks. They absorb how things work, just laying next to me. They get used to good thing happening when I'm around -- I randomly drop very high value treats and nibbles once in a while, just for laying next to me doing nothing but relaxing.
I've put some obedience on an ancient foster dog who was with me for months and months. She might have been 10 years old--maybe even older--and had always lived outside until my house. It was challenging because she didn't know how to learn. She didn't connect cause and effect with treats, or anything else. It took me 3 months to get her to sit for a treat -- and the moment she realized what I'd been trying to get her to do, her whole face lit up with joy as she connected it. From there on out it was like training any dog. The true challenge was learning how to learn, as that has to happen at whatever pace the dog's own brain sets.
She learned house manners more quickly by copying my other dogs -- I think she instinctively understood how to do that from living with other dogs, and wanted to fit in with them (pack instinct), so she peed and pooped outside exactly where they did, and did all the good things inside they did. Rely on your other dog to help model good behavior!
So take baby steps, build a bond, develop trust, and expect nothing yet. Let him decompress from living on the streets for a few weeks. He needs to watch your household routine, absorb it and get comfortable. There's a method called a "2-week shutdown" that many rescuers use (you can find many threads about it in the archive), but it's just a more rigid version of what I described, using time in and out of a crate.
Last edited by Magwart; 10-28-2017 at 10:07 AM.