Since there is no Sannin title, I feel as though it should be a suggestion to put such in anyway. For the members, I would suggest two per village. I understand that Anbu Captain takes on the Sannin title, but what about the Kages who step down from the Kage position and are still alive? Orochimaru, Tsunade (before she became hokage), and Jiraiya were Jonin that were the same rank as a Hokage and they were not Anbu Captains.
As I said, this is just a suggestion.
F.e. If a character has a main that's a kage from a different village and a alt that is a Jōnin in a different village and the anbu captain for the village that the jonin in is already taken, what if the Jonin that is A-rank wants to rank up, but the kage position for the same village as the Jonin is already taken as well? With both Anbu captain and Kage rank already taken, I think Jōnin (S-rank) should be a rank as well for Jonin that has the ability of a Kage for that same village.
As I said, this is just a suggestion.
F.e. If a character has a main that's a kage from a different village and a alt that is a Jōnin in a different village and the anbu captain for the village that the jonin in is already taken, what if the Jonin that is A-rank wants to rank up, but the kage position for the same village as the Jonin is already taken as well? With both Anbu captain and Kage rank already taken, I think Jōnin (S-rank) should be a rank as well for Jonin that has the ability of a Kage for that same village.