A 23-year-old man has been found guilty of murdering his stepfather and his 14-year-old brother guilty of his manslaughter.
Joshua Ellis, 23, and Jerome Ellis, 14, stabbed Neil Tulley, 54, to death as he lay on the sofa at the family home in Cedar Way in Guildford, Surrey, last August.
Mr Tulley, who was in a relationship with their mother Marie, was "asleep or nearly asleep" at the time of the attack, which was so severe he was nearly beheaded.
Jurors today found Joshua guilty of murder following a two-week trial at Guildford Crown Court.
The jury found Jerome not guilty of murder but guilty of the lesser charge of manslaughter on the basis of loss of control after deliberating for just over nine and a half hours.
Joshua was remanded in custody until sentencing on April 10.
The brothers had accepted they were involved in the stabbing but denied murder.
They had both argued that they suffered a loss of control which would also reduce the crime to manslaughter.
As he opened the case, prosecutor Philip Katz QC said it was not a matter of "black and white" as the brothers had a complicated family background with the adults described as "dysfunctional".
A year earlier Mr Tulley had threatened to kill Joshua and had swung at him with an axe, the court heard.
He was arrested and charged with making threats to kill but was acquitted by a jury - although he had admitted some of the behaviour.
He later returned to the crowded family home but by August last year the relationship between Mr Tulley and Ms Ellis had deteriorated and he was living on the sofa.
Mr Katz said of the brothers: "On the night of the 12th and into the 13th of August last year they acted together. They had killed Neil Tulley who was in effect their stepfather.
"Each of them was armed with a kitchen knife, a very large substantial kitchen knife, and stabbed Neil Tulley to death in what the prosecution would say was a savage attack in which he was almost decapitated."
Mr Katz noted that Mr Tulley was "asleep or nearly asleep" and added "there can not be any question of these two defendants were acting in self-defence - he was asleep".
A post-mortem examination confirmed that Mr Tulley had died from multiple stab wounds and found he had "65 separate sites of injury" across the whole of his body. The most severe wounds were at the neck, with one 8cm (3 inches) deep.
Jerome was also remanded in custody until sentencing after previously being on bail.
The brothers went on the run after the killing but were found hiding in a porch by a bellringer.
Joshua told the man that Mr Tulley "had been abusive and they could not take it any longer".
Jurors heard that after his arrest he told police that he had been "scared about what he (Mr Tulley) would do" - not just to his mother but also to his brothers and himself.
The elder brother had become a "virtual recluse" who was obese and withdrawn and living in the attic bedroom while Jerome was having problems at school.
Mr Tully, Ms Ellis, the two defendants and three other children were all living in the house.
A statement on behalf of Mr Tully's family was read out by Mr Katz, which said they were "devastated" by his death.
It said his mother had been left "traumatised" while his four siblings were "struggling to come to terms" with his murder.