The two teens have even claimed they saw their mother taking something that looked like drugs from a close confidant until they decided to no longer see her last summer.
Due to these concerns, the family allegedly planned an intervention for February 7.
The brood allegedly rented a "safe house" in L.A. and booked "interventionist" Matt Brown, who specializes in addiction treatment, although the plan soon collapsed.
"I don't want the boys to wake up one morning and find their mother has taken an overdose," Federline claimed.
Montgomery, who was appointed by the court to be in charge of Spears' affairs after the conservatorship concluded, had allegedly told Federline to prepare his sons for the event.
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While the father-of-two waited for word the intervention was underway, he received some bad news from Montgomery.
"Jodi just quit," Federline said at the time. "She said she can't do this any longer. She suggested I call the interventionist directly."
Shortly after, the Save Britney plan was leaked to the public, to which the "Toxic" singer adamantly denied on social media. Asghari has also denied any plan of an intervention for his wife of one year.
"This was the last chance for saving her. I am afraid that after that, another intervention will not be possible," another family member reportedly shared.
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Federline also claimed that he and the boys "have been through a trauma" in regards to the blonde beauty.
The two kids rarely, if ever, speak to their mother since they decided to stop seeing her last year. Jayden never answers Spears' calls or texts, Federline claimed. Meanwhile, Preston had a "good talk" with his mother December 2 to wish her a happy birthday, but has not communicated with her since.
The U.S. Sun reported on Federline's comments.