A struggle can be heard on a "gruesome" 911 call set to be released as evidence in the case of two brothers accused of stabbing their parents and three siblings to death.

A Tulsa, Oklahoma judge has entered not guilty pleas for Robert Bever, 18, and Michael Bever, 16.

Robert Bever, 18, and Michael Bever, 16, were each charged last week with five counts of first-degree murder in the July 22 attack. The older boy could face the death penalty; the younger boy faces only life in prison because of his age.

After entering not guilty pleas for the pair, who appeared via video from the Tulsa County jail, Special Judge Deborrah Ludi-Leitch set a preliminary hearing for October 28.

The brothers' lawyers declined comment, saying it was too early to talk about the case.

The city of Broken Arrow, Tulsa, Oklahoma, is planning to release records generated in the early hours of the investigation - including a recording of the 911 call made from the home placed by one of the victims.

Defence attorneys Rob Nigh and Cheryl Ramsey are seeking a protective order asking a judge to halt the release of documents they claim contain information that could be prejudicial to the brothers receiving a fair trial. A judge has scheduled a hearing on that order for Wednesday, a day after the city had planned to release the records to reporters.

Broken Arrow City Attorney Beth Anne Wilkening didn't immediately return a message seeking comment Monday on the release of the records. The attorneys for the brothers declined to discuss the protective order outside of court.

A Broken Arrow police sergeant had described the 911 call as "gruesome" last week.

"They're able to confirm the location, and then it basically goes to an open line for a little while and you can hear a struggle there and then it disconnects," Sergeant Thomas Cooper said.

Broken Arrow police went to the home late July 22, summoned by a faint voice on a 911 call saying a brother was attacking the family. A 13-year-old sister, who survived, told police that "her brothers" were responsible, according to an affidavit filed ahead of the pair being formally charged. A 2-year-old sister survived unharmed.

The boys were arrested shortly after the attack in a wooded area near their home. Police said a tracking dog followed their scent after officers noticed fresh footprints in the home's back yard.

The state medical examiner identified the dead as David Bever, 52; his wife April Bever, 44; and their children Daniel Bever, 12, Christopher Bever, 7, and Victoria Bever, 5.

Police haven't released a motive.

- AP