A Los Angeles judge has resentenced two brothers who are serving life in prison for the 1989 murders of their parents in a Beverly Hills mansion, making them eligible for parole.

Judge Michael Jesic gave Erik and Lyle Menendez a new sentence of 50 years to life. The brothers will now have to argue for their release in front of the state's parole board.

The pair acknowledged killing Kitty and Jose Menendez, but said they acted out of self-defence after years of abuse.

Prosecutors argued the brothers planned the shotgun killings to access their parents' fortune, are yet to take responsibility and should not be released. The case, which has prompted books and documentaries, still divides America.

After the judge agreed to resentence them, the brothers delivered an emotional statement to the court. They went through details of the brutal killings and their decision to reload and continue shooting their parents at point-blank range in their living room.

Both apologised for their actions and talked about their hopes to work with sex abuse victims and help those incarcerated if they were to be released.

"I had to stop being selfish and immature to really understand what my parents went though in those last moments," Erik Menendez told the court.

He describes the "shock, confusion and betrayal" they must have felt seeing their sons holding guns and opening fire.

Lyle Menendez's voice cracked as he talked about the impact of his "unfathomable" actions on their family.

"I lied to you and forced you into a spotlight of public humiliation," he said to his family.

He said they had "cried with me and expressed their suffering" and he was "grateful for your love and forgiveness".

Judge Jesic called the brothers' work while in prison "remarkable", but noted their original sentence was justified at the time.

He said under the guidelines, they were eligible for resentencing, issuing his new sentence of 50 years to life. The brothers have already served more than 30 years in prison.

The brothers' lawyer Mark Geragos said "today is a great day after 35 years". They were "one huge step closer to bringing the boys home", he added.

Anamaria Baralt, the brothers' cousin who testified inside court earlier in the day, said their family was elated.

"It is a difficult process," she said of the parole hearing that awaits the brothers, but noted they will "eagerly step through those doors if it means we can have them home".

Inside court earlier, relatives pleaded with the judge to allow the siblings' release.

Ms Baralt, who said she has been close with them since they were children, told the judge they deserved a "second chance at life".

"It's been a nightmare," she said. "I am desperate for this process to be over."

Ms Baralt told the court she speaks with the brothers frequently and testified that they had taken "ownership of their actions".

She said Lyle Menendez had acknowledged to her he had asked a witness to lie when testifying at their previous trial.

But she added: "They are very different men from the boys they were."