I would like the concept that Pohatu after they became Toa was the only one that knew Kopaka was a Prince/King, but did not thouch upon that subject with anyone else due to a deep respect and trust Kopaka and Pohatu have for each other (being friends even before they became Toa) and waited for him to open up about it.
In my concept, Pohatu comes from a humble background where people are more open towards each other and are generally nice for survival reasons. His upbringing behavior lead to him later to have the specific qualities of becoming friends with someone like Kopaka, despite Kopakas many flaws and many the times he was trying to push away any company because of his demanding role as future King of the Ice Kingdom.
Pohatu is the only one that can calm Kopaka down during the biggest problems, because they are nakama ( friends who are more like family).
The Forgotten God, I have a concept where priest Kivoda (pre-Toa Gali) found bits and pieces of the existence of a Seventh God...lets just say the majority did not believe her as much until finally the Lightning Empire revealed itself during the civil war, and the reveal of Voriki the 7th Toa.