Aztec mythology have a lot of different histories. Some say that he was brother of Huitzilopochtli, Tezcatlipoca and Xolot, others said that he was only the brother of Xolot. Some myths said that he and his bother/brothers were born of Ometecuhtli and Omecihuatl, while others claim that they have been born of Coatlicue (in a separate myth, it's said that Coatlicue gave birth to Huitzilopochtli alone).
However, all myths claim that all of them were not only brothers, but twins. In a myth the four are named Tezcatlipoca, but they are from different colors: White (Huitzilopochtli), Black (Tezcatlipoca), Green (Quetzalcoatl) and Red (Xolot). Interesting too is that this four deites are the contrapart of each one, as an example, Huitzilopochtli is the god of the Sun, while Tezcatlipoca is the god of darkness.
I can't really say if Michael will put them as somehow related due to the diversity of the myths, but I'm really looking forward to more of the feathered serpent.
Also I found interesting that Huitzilopochtli and Quetzalcoatl were not only the protectors of human kind, but also contribute in their creation. But in the books both are Dark Elders, we know the reason of Mars to become a Dark Elder…but Quetzalcoatl?