The Four Great Houses of Nayos
(See my original post about kryptis noble houses for where I'm coming from for most of this, though a big chunk of the info there is outdated now.)
So Eparch's Nayos has four major houses: Nephus, Aurkus, Febe, and Mosyn are all named as the founders.
Several nobles also appear in the throne room. It's possible they are each indicative of a lesser house for each existing, perhaps ruling over territories across other parts of Nayos we haven't seen (and perhaps that means Heitor is of such a rank?)
That said, I think the four great houses provide an interesting split in responsibilities:
House Nephus and House Aurkus serve as military oriented houses, while House Febe and House Mosyn handle civil responsibilities.
House Nephus is fairly straightforward: it is composed of strong warriors and brilliant tacticians who would also go on to serve as officers of military. This was of course, run by Grand General Nephus, and its prominent members also include Deimos, Cerus, and Peitha, but with Nephus in exile from Zakiros alongside the rest of his house, it seems likely that Eparch and Labris placed the three siblings here in order to both give them status and to control them.
House Aurkus is composed of assassins and inquisitors, serving to root out dissent discretely and identify threats to the Midnight Throne before they take ground. Aurkus, as far as I can tell, has never appeared directly in-game, but mentions of him include him whispering in Eparch's ear or being horribly sadistic to inquisitorial targets. Kanaxai is, of course, the most prominent member of this house to us. There's also a subtle religious slant to this house in the use of "inquisitors"—Kanaxai's memory of Mosyn even calls her words blasphemies.
House Mosyn is composed of artists and creative talents. Mosyn herself was a singer and a painter, so we can extend these to the rest of the house. It's possible they also served as architects and builders for the kingdom. Mosyn is the only member of the house we know of, though it's possible there were some in-game simply left unstated. Mosyn was unfortunately assassinated by Kanaxai at Aurkus's orders.
House Febe is where things are a little nebulous. We have no clear indication of what role Febe held outside of his relationship with Mosyn, but based on the Temple of Febe and the way religion exists for kryptis as upholding Eparch and Labris as divine (the Thirst for Power book in particular invokes religious imagery for Labris as the "Mother of Nayos" using such things as a "chalice"), perhaps House Febe was the closest to clergy that the kryptis had? If so, they may also have facilitated intellectual pursuits alongside spiritual matters, making them suited to working with House Mosyn. As with House Mosyn, Febe is the only member of this house we know of with the possibility of unstated members. Despite his status under Eparch, he was an outspoken proponent of breaking away from Eparch's tyranny, up until Eparch had Deimos kill him in front of Cerus.
If my assumptions are correct, you could also then place Houses Nephus and Mosyn as largely secular while Houses Aurkus and Febe have more religious slants.
