"Should he ever break that deal, he would be on the line for millions," they added.
The deal comes after Mel is believed to have paid out £500,000 in legal fees.
According to TMZ, Mel and Belafonte will share custody of their six-year-old daughter Madison and arrange a schedule for physical care between them, but neither will pay child support.
Stephen, however, will get spousal support for the next three years.
The alleged truce, which still needs to be signed off by a judge, comes soon after the pair settled the domestic violence part of their bitter split.
The pair have also reportedly agreed to give Stephen access to the family home, in order to collect his personal belongings, before they sell the property and divide the profits equally.
Additionally, Stephen has agreed to destroy "any compromising videos" or sex tapes of the former Spice Girl - with Mel accusing her ex of secretly filming her and threatening to release the footage in a bid to ruin her career, in court papers earlier this year.
MailOnline has contacted Mel's representatives for publication.
The agreement comes after Stephen claimed Mel is withholding access to his step-daughter Angel, 10 - who is Eddie Murphy's biological daughter.
Just days after the Spice Girl, 42, settled her domestic violence case against him and lifted his restraining order, Stephen revealed he plans to take his ex back to court.
In an Instagram post on Sunday, the 42-year-old producer shared a picture of himself cuddling Angel, as well as his biological daughter with Mel, six-year-old Madison.
