Chewie is almost 6 months old. I began training him to potty outside about 6 weeks ago. I started by offering him a treat immediately after he went. I had to play with him outside sometimes for 20-30 minutes before he went potty, but then brought him back inside immediately and offered a treat. I also made a really BIG deal out of it also--probably looked ridiculous.
Any way, persistance is key. This past weekend he actually went to the back door and scratched to be let out--made a really, REALLY big deal out of that one. I think maybe he's getting the point.
I know you have two dogs, but I don't think I would give your guy a treat unless he actually did something to earn it--like going potty outside. You might confuse him otherwise. He will learn quickly and it's a "call and response" treat.
Good luck and hang in there.