We don't know that.
We don't know whether Markec from 8th century Zagorje saw his great-great grandfather come from the same tribe as Dmitar from 8th century Biskupija's great-great grandfather.
Markec's ancestor who arrived in Zagorje could have come from an earlier migration from a different tribe.
Dmitar's migrant ancestor could have come with the Croats as a Croat, or with the Avars as a Slav auxillary.
We do know that all these Slavs spoke a similar language at the time as dialectization had yet to happen (and wouldn't form for another 500 to 600 years) yet belonged to VARIOUS DIFFERENT SLAVIC tribes.
We do know that Markec's descendants eventually became Croatianized as the Croatian name and ethnos moved north from Northern and Central Dalmatia and Lika towards present-day Zagreb.
We do know that Dmitar's descendants lived in the heartland of the Medieval Croatian kingdom and most likely fled to Zadar, Sibenik, or the islands when the Turks showed up.
That is all we know for now as the science isn't yet there for the rest.
Actually you are inventing new ethnicity which never existed in reality. No different language nor culture existed north of Gvozd mountain comparing to the south of Gvozd. The culture and ethnicity changes only north of Drava river where Hungarians begin.
We do know that all these Slavs spoke a similar language at the time as dialectization had yet to happen (and wouldn't form for another 500 to 600 years) yet belonged to VARIOUS DIFFERENT SLAVIC tribes.
Tribe is not an ethnicity! Ethnicity is about culture and language. Archeology does not see differences between two Croatian regions. Linguistics doesn't see different languages there in 9
th century.
Historical sources?
De Administrando Imperio; Chapter 30; Story of the Province of Dalmatia, 10
th century:
.
For a number of years the Croats of Dalmatia also were subject to the Franks, as they had formerly been in their own country; but the Franks treated when with such brutality that they used to murder Croat infants at the breast and cast them to the dogs. The Croats, unable to endure such treatment from the Franks, revolted from them, and slew those of them whom they had for princes. On this, a large army from Francia marched against them, and after they had fought one another for seven years, at last the Croats managed to prevail and destroyed all the Franks with their leader who was called Kotzilis.
Historians identify
Kotzilis as Frankish Duke of Friuli Cadolach (
Cadalaus):
.
Cadolah (or Cadalaus) (also Cadolach, Chadalhoh or Chadolah) (died 819) was the Duke of Friuli from 817 to his death. (...) By then he had been put in charge of Dalmatia, where he was the local ruler at the time when an embassy from Constantinople passed through on their way to the court of Louis the Pious (816). Sometimes after that, probably in 817, he was created Duke of Friuli. Einhard calls him Cadolaum comitem et marcæ Foroiuliensis præfectum ("Cadolah, count and prefect of the Friulian march") in 818. Einhard later calls him dux Foroiuliensis when recording his death after returning from a campaign against Ljudevit Posavski in 819.
http://dbpedia.org/page/Cadolah_of_Friuli
I assume that you know of which part of Croatia Ljudevit Posavski was the local ruler.