Great idea*, poorly executed.
Twins Connor and Grace are left penniless orphans when their father dies. To escape the rich couple that wants to take them in (and the orphanage that is their only other option), they steal their father's yacht and sail away.
After being caught in a storm that destroys the boat, the twins are picked up by two different ships. Connor is picked up by pirates and Grace is picked up by the (bum bum buuuuuum) Vampirates.
A few things. The prose is, well, kind of painful. I never got drawn into the story because I felt battered by groaner after groaner:
"...he had never gotten used to the raw power of the ocean -- its ability to change from a calm millpond one moment to a raging furnace the next." [Raging furnace? Like, flaming and hot? Bizarre.]
"She stared down at his bright green eyes. They were the exact same shade as hers -- as if an emerald had been cut in two." [I hate the gemstone-eye bit, especially when I'm supposed to like a character. Gemstones are hard and cold -- Kathy Mallory has emerald-green eyes, but she's a bit of a sociopath, so it works. The Tempest (yep, Tempest) twins, not so much.]
That's probably just personal taste, though.
This is another story. Recognize the captain?
The captain walked around Connor, without saying anything. Connor marveled at the many colors in his hair. At first, he had thought it was simply different shades of brown, but no, there was gray in there -- or rather silver, and then, as the light caught a fresh angle, green, too -- like strands of seaweed. Among the distorted rainbow were two -- no, three -- dreadlocks, bound with seashells. It was an unusual look, but he carried it off with manly ease. For all his finery, and somewhat erratic way of moving, you could tell that the captain had physical strength, not to mention the charisma of a natural leader.
Oh, but it COULDN'T be Captain Jack Sparrow, because Captain Molucco Wrathe wears glasses and has green streaks in his hair (one of which turns out to be a pet snake). Totally original creation.
Finally, I would like to know why the book needed to be set in 2505. Culturally, the pirates are a throwback to the early 1700's, there's nothing new technologically, and Connor is obsessed with hockey and basketball, says "cool" on a regular basis and high-fives people. I think there was vague mention of a catastrophe that affected the size of the oceans and technology in general, but nothing concrete. It just seemed like a sloppy way to allow the twins to act somewhat like modern teens AND have a pirate adventure.
I rather suspect that several sequels are planned. Eeek.
*Though I believe this came first.