Very good point.
My wife's dog likes to bark at everything under the sun. So when I was first walking Grim, we took 1-2 walks with the whole pack to get him OK with walks. After that, I stopped walking him with the girls because I didn't want him picking up bad manners. Now, I find him trying to calm my wife's dog when they're out in the yard and she's barking at nothing. Anytime you add in a new pup, it's a good idea to look at any 'bad manners' with your other dogs that you don't want the new one to pick up. Still, Grim only barks rarely. He's always looked to see what the girls are barking at (nothing) then walks away or blocks my wife's dog until she stops barking. (Note-she wasn't like this before, but has become this way in her old age, which is why we haven't been too hard on her about it)