Impossible series

When seventeen-year-old Lucy discovers her family is under an ancient curse by an evil Elfin Knight, she realizes to break the curse she must perform three impossible tasks before her daughter is born in order to save them both.

Phoebe, a member of the wealthy Rothschilds family, befriends Mallory, an awkward new girl in school, and the two become as close as sisters, but Phoebe does not know that Mallory is a faerie, sent to the human world to trap the ordinary human girl into fulfilling a promise made by her ancestor Mayer to the queen of the faeries.