The Inheritance Games by Jennifer Lynn Barnes

Avery Grambs has a plan for a better future: survive high school, win a scholarship, and get out. But her fortunes change in an instant when billionaire Tobias Hawthorne dies and leaves Avery virtually his entire fortune. The catch? Avery has no idea why--or even who Tobias Hawthorne is. To receive her inheritance, Avery must move into sprawling, secret passage-filled Hawthorne House, where every room bears the old man's touch--and his love of puzzles, riddles, and codes.

Unfortunately for Avery, Hawthorne House is also occupied by the family that Tobias Hawthorne just dispossessed. This includes the four Hawthorne grandsons: dangerous, magnetic, brilliant boys who grew up with every expectation that one day, they would inherit billions. Heir apparent Grayson Hawthorne is convinced that Avery must be a con-woman, and he's determined to take her down. His brother, Jameson, views her as their grandfather's last hurrah: a twisted riddle, a puzzle to be solved. Caught in a world of wealth and privilege, with danger around every turn, Avery will have to play the game herself just to survive.