Minato can't be Sannin...
Sannin was a title given to Jiraiya, Tsunade, and Orochimaru.
San = 3
Nin = Ninja
^ They became the Sannin of the Hidden Leaf due to how strong of a combination they had. I believe Hanzo gave them the title.

So it would only be Hokage unless he isn't wearing the cloak? then maybe some for of Jonin Minato(if there even is another version)