Yeah but the name 'Sannin' were give given by Hanzo. It is not a rank more like title. But again we can assume they are because i know Kishi' wants that.
:scorps:i hope they are all deemed sannin at some point by somebody who puts that same 2 and 2 together ya know?... lol.. sakura just has to sign a summoning contract and then learn how to sumon the slugs... all that after sasuke becomes good again anyway... and then once they are deemed sannin naruto will go on to be a supreme kage above all the individual kages... all there decisions and problems and matters will go through him...