On July 30, a day Britney Spears spent sipping Starbucks, shopping and lying low at her Beverly Hills home, her two-year marriage to Kevin Federline legally ended. The financial details are sealed, but the exes have agreed to share custody 50-50 of 22-month-old Sean Preston and 11-month-old Jayden James. "It's amicable," says Spears's lawyer Laura Wasser.

For the moment. As a source close to Federline, 29, says, "Once the ink is dry, look out." Federline, says the source, is ready to "go to court tomorrow to seek full custody" if Spears, 25, who spent a month at Promises rehab center earlier this year, does not follow the steps of recovery.

Not helping matters is Spears's recent erratic behavior—like bolting from a photo shoot after allowing her dog to relieve himself on a designer dress—and the frenzied atmosphere that surrounds her. While in Las Vegas last week, her bodyguard allegedly scuffled with two photographers, and one claims that Spears threatened to kill him. Federline, who had not been notified of her out-of-state travel with the kids as required by law, pressured her to return and, says a source, is "more than concerned." But Spears's longtime pal and former assistant Alli Sims says such scenes are an unfortunate result of a life in which Spears is "always being chased." Sims adds, "She's a wonderful mom and she is so hands-on." Those close to Federline fear that's not the case. "[Spears] puts soda in [the kids'] bottles," says one source. "She doesn't know any better, and no one is stopping her. She is good when they are good. She freaks out when they cry."

Meanwhile, Spears too is making noises about amending custody. Says a source close to Spears: "Britney believes when the kids are with Kevin that they're spending more time with the nanny." Counters a Federline friend: "The nanny is around to help out, but it's Kevin who wakes up in the middle of the night to calm and feed the boys." Adds his attorney Mark Vincent Kaplan: "He is a great dad, very structured. [The kids] are crazy about him." It is one thing he and his ex have in common. "Britney loves those babies to death," says Sims. "And they adore her."

  • Contributors:
  • Bryan Alexander/Los Angeles,
  • Howard Breuer/Los Angeles,
  • Jen Garcia/Los Angeles,
  • Marisa Laudadio/Los Angeles,
  • Mary Margaret/Los Angeles.