I've known about this case for years, but recently watched the Monsters TV series based on the case, which is basically a lightly fictionalized docuseries.
This instead is a documentary, with footage of the real trial, and with the brothers' narration. I recommend watching this documentary after watching the Monsters TV series, to get a more complete picture of the dynamics.
In this documentary, they want you to be more inclined to believe the siblings' abuse, and they succeed at doing it. I can't say whether I believe in the abuse or not, there is evidence that it happened, and at the same time there is evidence that they lied and pretended about many things, one thing does not exclude the other. But one thing is certain, both in this documentary and in the Monsters series, the second trial was not done correctly, it was not carried out guaranteeing a fair and impartial trial, it was carried out starting a priori that the only possible output would be the life imprisonment.
The Menendez brothers killed two people, and for this they deserve to serve a long sentence, but they do not deserve to be deprived of the right to a fair trial.
If their trial had taken place today, they would probably have already finished serving their sentence.