How can I break my dogs of a new bad behavior?

A new roommate and I have just moved in together, along with our 60 lb dogs. We’ve both never had problems with them, but now that they are together, we’re having issues. THEY get along fine, but when we walk them together, they bark and lunge at people we meet on the street, and generally sound like they want to kill someone. This is not ok. If we walk them separately they are their usual happy go lucky selves and perfectly behaved. But get them together and we’re “those girls with the jerk dogs.” We don’t want to be those girls! How can we break these newly formed bad habits?