It takes a little time, but the pack figures out the places. Some dogs are happy being lower ranked and others are not. Much like people, some are natural leaders and some are not. Sometimes it can get violent, but this usually doesn't last for long. Usually one or two confrontations is all it takes.
Usually ... but not always. Any of us that have done rescue and had multiple dogs in changing pack dynamics knows that once in a while you come across a dog that simply will not adapt to life in a pack. Just as there are people who cannot deal with society. I believe there are antisocial, reclusive, sociopathic dogs just as there are people. I have one living in my boarding kennel right now, as a matter of fact, because two years of intensive training and behavior modification has made not one bit of difference in his nasty attitude. My sister has two Siberians that hate each other, and have from the moment they laid eyes on each other six years ago. She has to keep them separated at all times, or they will kill each other. I've taken in rescue dogs that I simply couldn't keep ... they hated all the other dogs and caused nothing but problems, despite extensive efforts. It's not always possible for a dog to live in a pack situation.

And no offense to Molly or Mike, but I honestly would not want to have my dog living with 20 other dogs either. It may work with some dogs, but I think it could overwhelm others, and they just wouldn't be happy ... If Ash doesn't feel that Chewy would be happy with a bunch of other dogs, I don't see why we can't just listen to her...he's her dog, she knows him best.
I have many dogs who could live with twenty other dogs, and think it was a dream come true. But I have a couple dogs that couldn't handle it ... they can barely handle living with ten other small dogs. And I've had to send rescue dogs to another foster home because they absolutely couldn't deal with eleven other dogs. There are no hard and fast rules. I agree with your comment, not all dogs could handle this situation. I didn't take your comment to be offensive, just realistic. We don't know Chewy, we don't live with him ... Ash does.