The jury also convicted michael bever of one count of assault and battery with intent to.
Webrobert bever, who was 18 at the time of the killings, pleaded guilty in 2016 and was sentenced to life in prison without parole.
Michael bever was convicted in may.
Webmichael bever is accused of helping his brother, robert bever, kill their parents and three of their siblings in their broken arrow home in 2015, when he was 16.