I know the video says sleddogs, but those look like a pack of Lurchers to me- working sighthounds bred to work in a pack and course hare and rabbit. I know a woman from the UK who's family owns a similar pack of hunting beagles. If it's the same thing, the dogs are not only all raised together, they're actually *bred* from the other members of the pack (with studs being outcrossed, of course) with the puppies being integrated into the group at a young age. The older dogs then help teach the younger ones what to do. I've seen pictures of the young beagle pups, they have collars that are coupled, two by two, and they just attach the puppy to the adult until they learn for themselves what to do.
I'm willing to bet this is a similar situation, especially since the shape of all those dogs look like sighthounds to me!