First-degree murder charges have been formally filed against two Oklahoma brothers accused in the stabbing deaths of their parents and three siblings.

Tulsa County District Attorney Steve Kunzweiler's office filed the charges Friday against 18-year-old Robert Davis Bever and 16-year-old Michael John Bever. Court records did not show whether the brothers are represented by an attorney.

Each of the brothers is charged with five counts of first-degree murder and one count of assault and battery with intent to kill. The assault charge involves multiple stabbings of a 13-year-old sister who survived the attack.

They are accused in the July 22 deaths of parents David and April Bever and siblings Daniel, Christopher and Victoria. Kunzweiler's office has said Michael Bever will be tried as an adult.