1)
What is the meaning of "Kohanim"?
1.
Radak: They were officers of Kehunah. It seems that here does not discuss Evyasar ben Achimelech, for Shlomo banished him to Anasos (2:26)!
2.
Ralbag, Malbim: It is Kohen Gadol. Even though Shlomo banished Evyasar to Anasos (2:26), when Tzadok could not serve, Evyasar would serve 1 .
1
Why didn't Shlomo find a different Kohen to substitute? Perhaps it is because one who served as Kohen Gadol cannot serve against as a Kohen Hedyot (Yuma 12b); Shlomo did not want to Mevatel another Kohen from serving constantly, due to the rare occasions when Tzadok could not serve. (PF)