The question probably isn't so much whether royal vorpyr blood is necessary. That was definitely established in this chapter if not previously. The question is how does one become a royal vorpyr to begin with? Somehow having a third vampire seems to make this possible?

No, that was for resurrecting a "bits and pieces" vampire

Wrong. It was both. http://www.sluggy.com/comics/archives/daily/151116

And again here: http://www.sluggy.com/comics/archives/daily/151214

And I just noticed something I hadn't caught previously in digging up the second link. "With only two of us we can't make you a queen." So that pretty much eradicates other possibilities. Daryl says with only two they can't make her a queen. Sylvia says with three they can rebuild the Vorpyr. There's no mistaking it. With three they can make a king/queen and use the king's/queen's blood to make new vorpyr.

However, I can't help but wonder what the effect of making a new circle with a new king would have on the magical contract...