i read it. maybe. wiki is writtedn by people just like you and i. youn have to check the source material.Where does it say they knew?
Also, IF the Hidden Rain is their headquarters then Itachi/Kisame had to be in the Hidden Rain. Did you not read what I quoted from the Naruto wiki? Tobi reveals the statue to be in the Akatsuki headquarters.
EDIT: Unless it meant Tobi's or Kabuto's or something. Do they have headquarters?
and are you following the manga? or are you behind. just wondering. or anime. doesnt matter. it's not stated at that time, but we know, kisame knew, as we find out later on. so did itachi. so did pain and konan, and zetsu of course. we as readers didn't know that tobi wasnt tobi that time, but there's no reason akatsuki shouldn't have. i'm sayiinkishi might have made a litle mistake.
or short answer . we find out later that of those five, they all knew