The Sirius pack was surrounded by three packs that had formed from the Royals of the past. They were the three that didn't leave the Royals when the war had raged on centuries ago. And they were also the ones that knew the depth of the Royals' mission. Partly the reason why humans in the capital of Sirius were so comfortable living with them.
A hierarchy had been established to maintain the order amongst the werewolves with the Royals at the very top. The King's Beta alphas were ranked above all the other alphas in Sirius. They didn't form packs either as their main priority was to serve the king. Beta alphas, albeit powerful, lacked the power to defy the king even if he was only voicing his opinion of something. It was cruel, but also a consequence of the Royals of the past trying to control the bloodthirsty werewolves.