A. They use the portals of other angels who are killed by either Cameron or Janos (when he was still good) or Detective Costa (who uses a piece of Cameron's sword with his blood--a weapon with the blood of a good angel and owned by a good angel). Janos also later caused the death of angels using the plague in earth to create more portals to bring more Vampire Guardian Angels down from Heaven.
In addition, male babies who die on Earth resurrect in Heaven as full-grown angels, are bitten by the Vampire Guardian Angels, and become part of the Vampire Guardian Angel army.
Q. How do Vampire Guardian Angels control Earth Vampires?
A. They enslave humans for food and provide then to earth vampires -- in other words, earth vampires don't have to work for their food. They now rely on the Vampire Guardian Angels--their new masters-- to feed them as long as they do what the angels want them to do, including becoming part of their army on Earth. The earth vampires also cannot kill or harm a Vampire Guardian Angel since they are more powerful, so they fear them.
Q. What is the Vampire Guardian Angel society and hierarchy like?
A. Vampire Guardian Angels still go by a medieval, feudalist society and system where they are ruled by a King, and must loyally obey and follow. The nobles act as right-hand men and army captains, the rest are soldiers. The nobles and royalty doled out humans or material goods such as guns, swords and jewelry or gold as rewards. A fealty oath is taken during the homage to the newly ordained ruler. Technically only a royal could become ruler, but so could a Vampire Guardian Angel who possessed great power (such as Joseph’s “power of light” and Cameron’s ability to stop angels from ascending) and whoever possessed the author Ms Price, in combination with those powers.