Songs of Seraphina

the long version

"Three sisters are sent from America to England to live with their eccentric grandparents after their mother disappears and their father falls to pieces. But before the girls have time to find their feet, Charlemagne is married off to a dead man, Penny takes a nap and wakes up as a boy, and Cairo is swept into a dangerous romance with a man who wants her for more than her considerable charm. With the girls wrapped up in a conflict they barely understand, they don't notice that their grandmother is transforming, or that the two demigod assassins who took their mother are now coming for them--if one of them can get over his crisis of conscience."--From publisher's website.