In 2 Samuel 8:18 it says:
VeBnei David kohanim hayu
English translations translate the word kohanim as "chief ministers" or such titles.
Any clarification? I'm confused since only Aaron's descendants are allowed to be kohanim.
In this context, most (if not all) commentators explain that kohanim means high-ranking, respected, people.
One useful tool is comparing psukim from these times with their equivalents in Divrei Hayamim, which in this case (Divrei Hayamim 1, 18, 17) quotes the passuk almost word for word (translation from here):
וּבְנֵי-דָוִיד הָרִאשֹׁנִים, לְיַד הַמֶּלֶךְ ...
... and the sons of David were first at the king's hand.