My thinking is that the blonde gorosei is the patriarch of the vinsmoke family. The gorosei appear to be at the top of the Navy chain of command, yet not bound by its institutional rules.
From their chat with Akainu, it almost sounds like the Gorosei are the Celestial Dragons' liaisons into the world government (although they act more like a board of directors, liaison is too weak a term).
Perhaps the Gorosei are all politically active dragons. While most dragons live carefree lives doing whatever the hell they want in isolation, the Gorosei are their power brokers who extend the dragons' reach into the navy, key economic institutions, and yes, the underworld and world of piracy. Or if not the dragons themselves, then powerful families who have bargained their way into seats of power under the guise of serving the dragons, but who secretly have their own ambitions.
