Encyclopedia Eorzea Wrote:Imperial Court
The Garlean royalty are all of the line of Galvus. In addition to the aforementioned "zos," the term "yae" refers to male members of the royal family in the line of succession, as well as the Emperor's wife and mother. There also exists the title of "wir," or those who have no claim to the throne such as female heirs and their spouses. It is believed that all members of the royal family dwell within the extravagant imperial palace in Garlemald, and have decadent villas outside of the city.
Encyclopedia Eorzea Wrote:The Senate
The Senate ruled Garlemald during the days of the Republic, and while since diminished, still serves as an advisory role to the emperor and his court. Members range from upper level public officials, titled "fae," to the highest-ranking princeps senatus- "iyl." The Senate also holds the power to remove the magistrates - the consul, praetor, tribunus plebis, aedilis, and quaestor. However, it has yet to use this right.
A large image of the completed Garlean Social Hierarchy Chart can be found here! This one covers the titles in far more detail than the compilation from Gubal. Note that the lore book lists ordinary citizens as "Bas" whereas Gubal lists them as "Ban." "Ban" is a typo.
Lodestone: Nael van Darnus Wrote:van Darnus boasts distinguished parentage in his sire, a founding figure of the Garlean Empire.
Encyclopedia Eorzea Wrote:The VIIth Imperial Legion
Having existed since days of the Garlemald Republic, the VIIth Legion became legend for its ferocity during the campaigns to unify Ilsabard. The first legatus was the father of Eula and Nael van Darnus, and remains a lauded national hero to this day.
These quotes above give us some insight into how House Darnus achieved Garlean nobility in the transition from Republic to Empire, but I just spent the last half hour combing google for some text I seem to recall from the 1.0 Lodestone suggesting that many of Garlemald's current "nobility" are members of the original founding Republic families. While this, in all likelihood, is not a requirement for nobility it could be a tidbit you consider when creating your own House of Garlemald.
It's then just a matter of deciding what position your character would hold in the Garlean hierarchy- and remember, if multiple titles apply to a single person, the higher title is always taken.
More lore on Garlemald and its history and military found outside of the lore book's pages can be found in this Garlean Lore Compilation. Hope this helps! ^^