Precisely.
But she would have to fall in love with her brothers enemy and sell him out.
Even if the hero is a blood drinking abomination.
Well, okay. It sounds challenging, but it might work out.
That said, we have now created on organization of formidable threat capability. Your vampires will have their work cut out for them.
You'll probably want to concentrate your artwork on showing the principal characters.
I think you would need to go back a ways to establish the "blood feud" origins between the groups, too.
Perhaps, sensing a potential adversary, the cabal was behind some attempts to rid the world of vampires.
One way to begin might be in comparing the recruitment procedures of the two groups, and emphasizing how they differ.
Or perhaps have a chance run-in between two really old adversaries, who each had thought the other dead, and now have to renew their efforts to control the situation.