Richard Smith stabbed his wife Clair in the chest and strangled her with a neck scarf before stabbing nine-year-old Ben and one-year-old Aaron at their home in Sheridan Way, Pudsey, in December last year.
He then placed the family on his bed, blocked the doors and windows and set fire to the mattress before lying down with them to die, Leeds Coroner’s Court heard.
The family were found on the bed with the ashes of baby Jake who died fours years earlier in December 2007.
The inquest heard that Mrs Smith, 36, died from the stab wound to the chest and compression of the neck and Aaron died from a stab wound to the neck. Both were dead before the fire started.
Ben had been stabbed three times, in the chest, neck and arm, but the wounds were not fatal. He died from inhaling smoke and fire gases and suffocation.
Dr Brian Rodgers, a pathologist who conducted post-mortem examinations on the family, said the suffocation could have been caused by a hand being placed over Ben’s nose and mouth or because his face was pressed tightly into his father’s chest as they lay on the bed.
Mr Smith, 37, a quantity estimator, died from smoke and fire gas inhalation but had also stabbed himself in the neck in an unsuccessful attempt to take his own life.
Detective Superintendent Paul Taylor, of West Yorkshire Police, told the inquest: “Clair was in the position you would imagine was natural to sleep in, Ben was laid across his mum, Aaron between them and Richard embracing all three.”
Mr Taylor continued: “Four years ago, almost to that day, they lost a baby Jake. The box containing baby Jake’s ashes was found in the crook of Clair’s arm.”
Mr Taylor said the couple would take days off work each year around the anniversary of Jake’s death.
Coroner David Hinchliff said: “That’s something that obviously deeply affected them.”
Mr Hinchliff recorded verdicts of unlawful killing on Mrs Smith, Ben and Aaron and said Mr Smith took his own life.
He said: “It would appear Richard has undergone some aberration, some problem, affecting his mental health which caused him to take the action he has.”
Mr Hinchliff added: “It was a concerted act of destruction of his family and his own self-destruction.”
He continued: “It is my view that, having been the perpetrator of all that had happened and being faced with the enormity of whatever was preying on his mind at the time and causing an aberration of this immensity, he has taken his own life.”
The family were found at the three-bedroom detached house in Sheridan Way on the evening of Sunday December 11.
Speaking after the inquest, Mr Taylor said they had attended a social event at a local cricket club two days previously, on the Friday evening.
He believed they died a short time later as Ben had not opened his advent calendar on the Saturday morning.
Mr Taylor described Mr Smith as “obsessive” and said he had been receiving treatment for depression for around two years.
He said something may have happened to cause Mr Smith’s actions which would not necessarily have affected other people.
He added that the anniversary of baby Jake’s death was also likely to have been a contributory factor.
Mr Taylor praised the families of Mr and Mrs Smith for their dignity.