The extended family of Erik and Lyle Menendez will advocate for the brothers’ release from prison during a news conference in downtown Los Angeles.

It comes as prosecutors review new evidence to determine whether they should be serving life sentences for killing their parents.

Billed as “a powerful show of unity” by more than a dozen family members — including the brothers’ aunt — who are traveling across the country to Los Angeles, the news conference set for Wednesday will take place less than two weeks after lawyer George Gascon announced his office was looking at the brothers’ case again.

Erik Menendez and Lyle Menendez (California Department of Corrections and Rehabilitation/AP)

Erik Menendez, now 53, and his 56-year-old brother, Lyle Menendez, are currently incarcerated in state prison without the possibility of parole after being convicted of killing their parents in their Beverly Hills mansion more than 35 years ago.

Lyle Menendez, who was then 21, and Erik Menendez, then 18, admitted they fatally shot-gunned their entertainment executive father, Jose Menendez, and their mother, Kitty Menendez, in 1989 but said they feared their parents were about to kill them to prevent the disclosure of the father’s long-term sexual molestation of Erik.

The extended family’s attorney Bryan Freedman previously said they strongly support the brothers’ release.

Comedian Rosie O’Donnell also plans to join the family on Wednesday.

“She wishes nothing more than for them to be released,” Mr Freedman said earlier this month of Joan VanderMolen, Kitty Menendez’s sister and the brothers’ aunt.

Earlier this month, Mr Gascon said there is no question the brothers committed the 1989 murders, but his office will be reviewing new evidence and will make a decision on whether a resentencing is warranted in the notorious case that captured national attention.

Erik Menendez, centre, listens to his lawyer Leslie Abramson as his brother Lyle looks on in court in 1991 (Julie Markes/AP)

The brothers’ attorneys said the family believed from the beginning they should have been charged with manslaughter rather than murder.

Manslaughter was not an option for the jury during the second trial that ultimately led to the brothers’ murder conviction, lawyer Mark Geragos previously said.

The case has gained new traction in recent weeks after Netflix began streaming the true-crime drama Monsters: The Lyle and Erik Menendez Story.

The new evidence includes a letter written by Erik Menendez that his lawyers say corroborates the allegations that he was sexually abused by his father.

A hearing was scheduled for November 29.

Prosecutors at the time contended there was no evidence of any molestation.

They said the sons were after their parents’ multi-million dollar estate.

But the brothers have said they killed their parents out of self-defence after enduring a lifetime of physical, emotional and sexual abuse from them.

Their lawyers argue that because of society’s changing views on sexual abuse, the brothers may not have been convicted of first-degree murder and sentenced to life without parole today.

Jurors in 1996 rejected a death sentence in favour of life without parole.