The Rise of Nine by Pittacus Lore

The Rise of Nine is a 2012 young adult science fiction novel by Pittacus Lore, the third book in the Lorien Legacies series, following John (Four), Six, and Seven as they find other Garde members, including Nine in West Virginia and Eight in India, to unite against the invading Mogadorians. The narrative explores themes of unity and hope as the Lorien survivors work to gather their forces before it's too late to save their world and Earth.