Dangerous allies / Lisa McMann.

Enhanced descriptions from Syndetics:

X-Men meets Spy Kids in the fourth installment of The Forgotten Five middle-grade fantasy/adventure series by the New York Times bestselling author of The Unwanteds.

Following an explosive showdown with President Fuerte and his supernatural henchmen, the forgotten five and their allies are feeling lost. Their trusted friend and mentor The Librarian has left the group and declared her loyalty to the corrupt president. Has the Librarian really abandoned them in their quest to take down Fuerte's regime, or has she been kidnapped?

Then, without warning, Troy Cordoba-Tenner's dad, who has been working for Fuerte for years-shows up at the five's safe house wanting to join their cause but accidentally leading the presidential guards right to their doorstep. Troy insists that he has changed for the better, but Tenner isn't sure he can be trusted.

Meanwhile, Magdalia Palacio's election campaign is gaining steam. If she's against the president, does that make her the five's ally?
The kids will have to decide who to put their faith in-and fast-before the president uses his supernatural army to crush his opponent and cement his criminal rule over Estero once and for all.