Akainu - Doflamingo - Kidd
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Kizaru - Vergo - Killer
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Fujitora --- Pica - Wire
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Ryukogyu --- Diamante/Trebol - Heat
I see Kizaru as the "vice captain", the only one Doflamingo or Kidd has utmost confidence in.
No need for Luffy to take out both Kizaru and Akainu. Kizaru like Vergo and Killer is a job for Zoro or an ally (Law, Sabo, new ally).
Fujitora is similar to Pica, the clear #3 guy that the captain uses but doesn't trust like his VC.
Ryukogyu, while a Admiral/Seat like Diamante, would be beat by Fujitora/Pica or even worse by Kizaru/Vergo.