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Yes, different indigenous people is no problem at all. Many countries have several indigenous people. In The Netherlands we have the Dutch, of course, but also the Frisians. A Frisian will say he is a Dutchman, but not a Hollander. They have their own official language, Frisian. It doesn't stop there. Limburgians have a different dialect, almost a different language. There are even more ethnic groups.
The Dutch are often called Hollanders, but Hollanders are indigenous of the provinces of North and South Holland, strictly speaking. Frisians live in the area of Friesland, Groningen and Northern Germany bordering the Netherlands. Frisians lived there before the Romans discovered Germania.
In Belgium you have 3 groups: the Flemish, Dutch speakers, the Walloon, French speakers and a German community (courtesy of WW1). The Dutch and French speakers are often at odds regarding the language. They were 'first' in their respective areas.
Plenty of countries have more variety. Switzerland for example. They have 4 different ethnic groups: French, German, Italian and a small other indigenous group: the Romansh. Each with their own language and customs. Schweizerdeutsch is somewhat different from Hochdeutsch. 4 different languages doesn't seem so much of a problem here as 3 in Belgium.
It is impossible to say who was the first. They probably all were, in their respective areas. It can but doesn't have to be a problem.