"Royalty" does not mean Celestial Dragon. All the the Yonko/Emperors are Kings/Queens and so are a handful of the Shichibukai.
Doffy is a King. Hancock is a Queen.
Yes, it does. The Celestial Dragons are descendants of Kings and Queens who ruled various countries during the void century that left to Mariejois after the formation of the World Government. They are
actual royalty.
The Yonko are
not. They are not legitimate royalty. They have their titles by what they took, not because of their bloodline. They’re no more royal than Roger was, who got his title because the World Government called him it out of nowhere. Big Mom was born to normal parents before being abandoned. Whitebeard was an orphan on a destitute island. Teach was an orphan.
Hancock is not a real Queen. She was a regular girl that got enslaved.
None of these titles are legitimate royalty. They’re based on what they took later, not their blood.
And Oden.
But yeah, the majority of the Pirate "royalty" aren't actual royalty. The real royal bloodlines in One Piece are the Reverie attendants and Celestial Dragons.
Basically, the vast majority of CoC users we've seen are Napoleon- real world Napoleon, not One Piece sword Napoleon. Oden and Doflamingo are the only ones from a royal bloodline, they'd be the Bourbon's.
At the most you can argue the D's are obviously some special bloodline that trace their ancestors back to the Amcient Kingdom, but there's no guarantee that lineage is royalty- would there be at least seven royal families from one kingdom? And even then, there's still plenty of CoC users who have nothing to do with royalty or the Will of D.
I left off Oden because I’m not sure how the shogun system works in general. If it’s something where you can be appointed, then it’s not really royalty I think. Oden’s dad said he wanted Oden to be the next Shogun, which is like an appointment as opposed to inheritance, right?
Even with Oden, if the shogun is indeed royalty as opposed to a simple appointment of someone to power, as you said and I said previously, the overwhelming amount of evidence shows that CoC has nothing to do with “royal bloodlines,” so this would clearly not support Sanji (the issue of the D. clan notwithstanding).