Why'd Sanji not be in command of his group as long as that group doesn't include Luffy or Zoro? Sanji is clearly third most important crew-member and second mate. He's a leader if Zoro and Luffy aren't present.
Idk why you're so bent on official. Zoro and Sanji aren't official anything. Theyre not officially above Chopper in leadership, either. Luffy's crew doesn't have an OFFICIAL hierarchy, but an unsaid one. We look at portrayal for hierarchy. Similarly, the VC confirms that Zoro is the one who ACTS like First Mate, not Sanji.