Los Angeles County District Attorney George Gascón announced his decision at a Thursday afternoon news conference.
"We are going to recommend to the court (on Friday) that the life without the possibility of parole be removed and they would be sentenced for murder," which would be a sentence of 50 years to life, Gascón said. But because of their age -- they both were under 26 at the time of the crimes -- they would be eligible for parole immediately, he said.
"I believe that they have paid their debt to society," he said. "The final decision will be made by the judge,"
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The decades-old case began on Aug. 20, 1989, when Lyle and Erik Menendez fatally shot their parents, Jose and Kitty Menendez, in the family's Beverly Hills home. Lyle Menendez, then 21, and Erik Menendez, then 18, used shotguns they bought days earlier.
Prosecutors alleged the brothers killed their wealthy parents for financial gain.
The defense argued the brothers acted in self-defense after enduring years of sexual abuse by their father.
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Their first trials -- which captured the nation's attention with cameras in the courtroom -- ended in mistrials.
In 1996, at the end of a second trial -- in which the judge barred much of the sex abuse evidence -- the brothers were convicted of first-degree murder and sentenced to two consecutive life prison terms without the possibility of parole.
The sensational case gained new attention this fall with the release of the Netflix drama "Monsters: The Lyle and Erik Menendez Story" and the Netflix documentary "The Menendez Brothers."
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Gascón said this month that his office was evaluating new evidence: allegations from a member of the boy band Menudo who said he was molested by Jose Menendez, and a letter Erik Menendez wrote to a cousin eight months before the murders detailing his alleged abuse.
Erik Menendez's cousin testified about the alleged abuse at trial, but Erik Menendez's letter -- which would have corroborated the cousin's testimony -- wasn't unearthed until several years ago, according to Geragos.
Nearly two dozen of the brothers' relatives united at a news conference last week to push for their resentencing.
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"Their actions, while tragic, were the desperate response of two boys trying to survive the unspeakable cruelty of their father," Kitty Menendez's sister, Joan Andersen VanderMolen, said. "As their aunt, I had no idea of the extent of the abuse they suffered."
"It's time to give them the opportunity to live the rest of their lives free from the shadow of their past," she said.
Behind bars, the siblings "sought to better themselves and serve as a support and inspiration for survivors all over the world," added Jose Menendez's niece, Anamaria Baralt. "Their continued incarceration serves no rehabilitative purpose."
The brothers "deserve a chance to heal, and our family deserves a chance to heal with them," Baralt said.
Despite the massive show of support, one relative -- the brothers' uncle, Milton Andersen -- is adamant about keeping them behind bars. He said in a statement he firmly believes his nephews were not sexually assaulted and were motivated by greed.
ABC News and the Associated Press contributed to this report.