I see what the person who wrote that post is trying to get at, but all the silly business about dominance and being an alpha or a pack leader kind of gets in the way, doesn't it? I'd say you could explain it much better yourself, Athe, without all the misleading and misguided jargon - personally, I think you're infinitely smarter than the person who wrote that!
The one germaine point to that article is:
3- When puppies are raised togther they become what we call DOGGY. This means they look at the other dog as their buddy and not the human that owns it.
That makes good sense. The pups are already bonded, and they're being taken away from everything they know, so they are naturally going to cling together and bond more strongly and depend on each other rather than on the strange smelling people who have snatched them up and taken them to a strange smelling place far away from mama and littermates and everything safe and familiar.
4- These dogs are more difficult to train. Because they don't have the strong human bond, they don't have the desire to please. In fact they often become stubborn.
That's really an elaboration of the "doggy" description. I don't know that 'stubborn' is the necessarily the right word, though. You are just not relevant to them. They get all the reinforcement and reward from each other and just don't need that human feedback.
All that said, if the person who wrote that was correct on all those counts, I'd have a couple of truly dangerous dogs on my hands right now! While I would never, ever recommend pups from the same litter (although Kharma's brother, Oliver, was a great temptation, lol!), my experience with two pups from different litters, with
some age difference between them is that the newer pup will try to catch up with the older pup, and the older pup will work harder to stay ahead. You can use their desire for your attention to your advantage, lol!