Well it starts when a mommy dragon and a daddy dragon love each other very much
So obviously we will see baby dragons.
Or they ignore each other completely which will probably lead to some dragons being stuck flying into each other and some you tube videos
Todd already said we won't be seeing baby dragons, during the newest interview. He even referred to the Dragonlings from Daggerfall, and said they won't be around, because they want us to fight big, menacing dragons, not babies.
Also, yes, they are allies with each other under Alduin. Todd even recounted when 3 of them attacked him at once, and how ridiculously hard it was. And no, they are not "animals". They are intelligent, they think, they speak, they use magic, and they aren't all going to fight you mindlessly. They may seem like beasts to the player, but they certainly have a lot of mind to back up the brute force.