Twins are born in the same sack. Trips are all in the same sack. Litter mates are what they are to each other, siblings, they rank from the most submissive to the most dominate. It is a pecking order.
You need to look further into this, dogs are really neat creatures. Learn about them. dog behavior, canine body language, training, learning to train, reproductive system, .... hope you find interest in this & continue to learn more about dogs.