Kind of shameless self-plug, but awhile ago (2.2) I did an experiment to try to discover which Tribes made their home in which region based off in-game NPC distribution. Ultimately, it was largely inconclusive, but it's on this topic and might be found interesting.
But there is no definitive lore on the subject, so feel free to shape your background and story however you feel is appropriate. ^^ But as far as I'm concerned, Miqo'te (per lore) traveled from the Western Continent to Aldenard 3000 years ago during the Age of Endless Frost (5th Umbral Era) and settled mainly in Vylbrand and Thanalan and in the 3000 years since that time, have come to be found throughout Eorzea and beyond. The 26 Tribes refer to those original 26 Tribes which made the travel, there's no telling how many times those Tribes have split or relocated since that time.
But there is no definitive lore on the subject, so feel free to shape your background and story however you feel is appropriate. ^^ But as far as I'm concerned, Miqo'te (per lore) traveled from the Western Continent to Aldenard 3000 years ago during the Age of Endless Frost (5th Umbral Era) and settled mainly in Vylbrand and Thanalan and in the 3000 years since that time, have come to be found throughout Eorzea and beyond. The 26 Tribes refer to those original 26 Tribes which made the travel, there's no telling how many times those Tribes have split or relocated since that time.