09/10/2007 at 01:00 AM EDT
Who babysits when a divorced dad and aspiring actor lands a role? For Kevin Federline
, 29, there was only one obvious—yet still jaw-dropping—solution: He got his ex-wife's parents, Jamie and Lynne Spears, to mind his kids while he filmed an episode of One Tree Hill in North Carolina. On Aug. 24 Lynne, 52, pulled up to Federline's Tarzana, Calif., home with gifts for Sean Preston, 23 months, and Jayden James, 11 months, and in the afternoon both grandparents took their charges on a stroll around the neighborhood.
If there was any question of strife between Spears, 25, and her family, her parents' voluntary membership in Federline's babysitters' club speaks volumes. Already bitter that her mother pressured her into rehab ("Lynne has used the kids as bait, guilting Britney into making decisions she regretted later," says a Spears pal), now "Britney's angry because Lynne sided with Kevin," says a family friend. Unable to see the boys with Britney, Lynne visits them at Federline's home, where Spears's dad, Jamie, 55—whose relationship with Britney has been strained since he and Lynne split in '02—also stopped by on Aug. 16.
Spears's isolation from her family comes when she could use a lifeline. The Britney vs. K-Fed custody fight took a darker turn at an impromptu hearing Aug. 27, which focused on a complaint that the L.A. County Department of Children and Family Services received questioning the safety of the couple's sons. The fact her parents, after their own contentious divorce, are now presenting a united front reflects the severity of the rift. But Spears isn't likely to budge any time soon. "We always push Britney to make up with her mom," says her friend, "but she feels like she can't trust anyone. [The babysitting] is just another example of that mistrust. It's only making things worse."