idk, I feel like the tribes are more broad then that, tribes in minmatar society are basically analogous to their nations and ethnic groups. the word tribe is probably fairly inaccurate in judging the actual thing.
think about it this way, the minmatar were not a unified world when the amarrians invaded, they still had their countries, which would be the tribes. Now that the rebellion has happened, the government is essentially unified, but homogenization hasn't had enough time to break down the social barriers the way it has in the other empires, the people still can trace their ancestry back to their parent "country" basically, imagine that Europe is invaded by imperialist catholic Russia, eventually, they push russia back out, and unify themselves together as one government to present a strong enough front to resist the russian slavers who just want to burn them all. But the old countries are still there in a sense, the people still claim to be part of them. Thats sort of how I see the matari tribes.