When teaching a young pup or inexperienced dog, I would recommend teaching one by himself...how to walk nicely on a loose leash. At least get a good handle on it before taking them both together. If one pulls and the other doesn't and you need to stop and/or turn back the other way... to show the pulling one that the walk won't continue if he pulls, the one who is not pulling gets the reinforcer of getting to continue walking taken away from him.
Once they learn that any tension in the lease won't work for walking, but a loose leash will work, then try them both together, but in a distraction free environment until they're good there. Then gradually add in more distractions. Make sure to frequently reinforce nice walking. Reinforcement = continued walking and a super duper treat. (tiny) Show your dog what works and what doesn't. Be consitent. If you pull on the leash, the dog's opposition reflex will kick in and he'll pull too. (not because he's stubborn or dominant) One step of forward motion when there is no slack in the leash not only reinforces the behavior, but puts it on a variable reinforcer which strengthens the behavior you don't want.
Mark the correct behavior with a special sound or clicker, then treat. You can Google Clicker Solutions and read about clicker training. (an excellent way to communicate and give explicit feed back to your dog so he learns) (lots of good training articles)
I walk all three of mine together, but not every time we go for a walk. But they're 7, 9 and 9 yrs. old and don't tend to pull. Sometimes, just at the start of the walk, Jose` will pull a little. He's an eager beaver. So, I'll stop and the other two get "penalized" too. That's not so good. But, after one or two stops, he gets the hint. Then we all walk fine. I usually walk the big dog on my left and the two Chihuahuas on my right, each with their own leash. The little ones wear a harness and the big one wears a flat, leather collar. They can walk on both sides though. I sometimes vary it to keep them on their toes.
From Clicker Solutions:
ClickerSolutions Training Articles -- Loose Leash Walking: The Total Picture