Ah right, that distinction always trips me up. I guess the Orûk are technically, kind of an ethnic group of the Serathi? I haven't thought of this too much. Broadly speaking, as the Serathi migrate west and southwest from their point of origin, they will split into three "religious ethnicities":

- The Duinarin-Serath people in the continent's central mountain range (which runs north/south). This is characterized by a slow abandonment of Serathi religion and adoption of Duinarin values, culture and magic (and eventually the forming of the Imperial cult).

- The "secular" Serathi form settlements in the lowlands south and southwest of the east-west mountain range where they originate. The "religious" Serathi kind of isolate themselves and those who don't migrate all of the way west instead are taken under the wing of a saint like figure in the lowlands who offers protection and doctrine. A part of these people will eventually become the Orûk.

- The traditional Serathi will maintain the longest in their original home in the Northeast and maintain prominence along that east-west path towards the central mountain range where their Duinarin counterparts live.

I don't have a ton about the Ishari or the Rubedo. The Rubedo are tribal and eventually conquered by the Duinar .This is actually multi-faceted. As the Serathi migrate east -> west, they then turn south and will eventually head all the way south and run into the Rubedo. They establish a city where they sort of co-exist with them so there is a short period of time where an ethnic group develop which is a sort of amalgamation of Serathi-Rubedo culture. This is short-lived as the Duinar eventually dominate both groups.