I walk both of mine together (and did the same when I had 3-4 dogs). I used to dog sit & assist at agility & obedience shows & classes etc... & there have been times when I'm walking 5-7 dogs.

I teach my dogs to heal but they also know to walk properly on a leash (not pulling or crossing each other all the time etc...), I call it "walk". If I don't mind if they pull & go crazy etc.. I just release them by saying "ok". Usually I just walk them like I would walk one as I rarely use the heal command. But I also taught my dogs to heal on the right side (I call it "side"). So if I need them to heal I can either have them both heal side by side or I can have one heal on the left side & I tell the other one "side" which is healing on the right side.