I doubt Sanji has it. Coby is paralleling Sengoku : so if he has it then surely so does Sengoku. So either they both have it or neither has it. It's highly unlikely all five Gorousei have Haoshoku Haki. Kidd is paralleling Shiki. Shiki didn't have Haoshoku Haki. But the one true leader thing is a lot of speculation bro...
1. I believe Sanji & Zoro are bound to develop their CotSK (well actually, I think Zoro actually does use it). Why? Because some of the users of CotSK have shown to possess a somewhat attribute/theme/trait which coincides with their power. E.G. Hancock's CotSK is what makes everyone swoon over her even more than they normally would, in addition to her looks. Her DF doesn't automatically make people go head over heels for her. It turns them to stone if they lust. Her COC is what makes them see her appeal. And therefore it's easier for her to be away with her enemies. Also Doffy's CotSK emphasizes on his "control" over other - the very thing his DF allows him to do.
So what does that do with Sanji & Zoro? Because Sanji has the trait of wanting women to love him, and most of the time, he fails at that due to putting-out too much. However, @FI, albeit he put-out, the Mermaid's still liked him. And I think this is because he developed his other Haki during the TS, so subconsciously (because Rayleigh said one cannot truly train their CotSK but can only improve their spirit/willpower to make it stronger) during the time he trained his CoO & A, sleeping CotSK became dormant. What's more is that Luffy's CotSK was unleashed when he calmed down Duvall's bull, and later extremely unleashed @MF, the very place he subconsciously used CoO. Thereby the mermaids were subconsciously struck by him. Additionally, this is supported by Violet; the first ever lady to actually be highly interested in him despite his horny personality. And that's the case because his CotSK is beginning to grow.
As for Zoro: He's CotSK became dormant @SA. Why? Remember when he was about to kill the CD? What happened? As he approached the CD while unsheathing his sword, the CD froze in fear, and what's his attribute? Fear/killing intent - as shown when he fought T-Bone, Kaku and recently, Monet. So, this means his CotSK is based on him inducing fear into his opponents. And since I think Mihawk has CotSK, he sensed it inside Zoro and told him how in it strengthened. And that's why he was able to beat Monet; because his CotSK didn't burst out subconsciously, but rather in a controlled manner.
Furthermore, remember what Rayleigh said about CotSK? He said those with big names have it. Nowthink back to TB. What did Sanji promise Kuma after Zoro told him that his head is the head that will be the WSS? He told Kuma his head will be the one all Marines will cower at. And someone who all Marines are scared of is surely a huge named person.
2. Coby paralleling Smoker and Kidd paralleling Shiki is also speculation. So it's not fact. And also, Oda paralleling the 'New Era' with the 'Old Era' is boring, bland and most of all, cliche'. Plus each error is meant to be unique on it's own right, so having characters follow the preceding one's isn't so much unique.
3. If a fodder like Chinjoa had it, I don't see why the Gorosei shouldn't.
