Well, when they taught Pehea kākou? to mean How is everyone?, that was a loose translation. The word kākou actually means we in a specific way. It means we, including you and me and other people, kind of like everyone. However, everyone cannot usually be translated as kākou, since everyone can be others except "me", for example everyone in my family likes grapes except me. In that regard, you cannot use kākou.