A Perth father is likely to die behind bars, after being jailed for life with an 18-year minimum for murdering his son Matthew Fisher-Turner in 2016.

Ernest Albert Fisher, 67, attacked his son from behind with two kitchen knives inside the Parmelia home they shared, stabbing Matthew up to six times, then left his children to bury the body so he could watch the AFL grand final.

He admitted fetching says his weapons from a garden shed and told police he “jumped on his son" and stabbed him hard to "make it count".

Ernest Fisher has been found guilty of the murder of his son, Matthew Fisher-Turner, in 2016. (9news)

He later claimed killing the 23-year-old was the "right thing to do".

During his trial, Fisher claimed he acted in self defence, to protect his family because Matthew was abusive and violent.

But today Justice Stephen Hall disagreed, and said he instead acted out of "hatred, frustration and anger."

Matthew Fisher-Turner was "abusive", Ernest claimed in court. (9news)

Joshua Douglas Fisher-Turner, 28, and Hannah Jayde Fisher-Turner, 21, were both convicted of being accessories to murder.

The court heard the family had been unravelling since the death of its matriarch in 2014, and the final straw for Fisher was when Matthew insisted on borrowing his car, which triggered an argument because he wanted to drive to friends to watch the AFL grand final.

After puncturing Matthew's lung and aorta with knives bought specifically for the killing, Fisher started digging a grave in the rear garden, then left the house to watch the match, leaving it up to Joshua to bury his brother, while Hannah helped carry the body outside on a ladder.

When friends and police became concerned about Matthew's sudden disappearance, Fisher initially claimed his son was "over east with a chicky babe".

Matthew's fully-clothed body was found after he was reported missing by friends. (9news)

But after about 90 minutes of questioning by detectives, he admitted he'd killed his son weeks earlier and told them he was buried in the backyard of the family's home.

Justice Hall said he accepted there were disputes and confrontations with Matthew, but whatever violence occurred was not of the severity or frequency to justify Fisher's actions.

When detectives interviewed Fisher, he rejected suggestions he could have taken actions such as obtaining a violence restraining order against his son.

"There were obvious alternative ways of dealing with that (violence) as you must have known," Justice Hall said.

Justice Hall said Fisher had shown no regret or remorse, noting he told police the sensation of killing his son wasn't pleasant, but also remarked he'd "done the right thing" and continued to say derogatory things about Matthew.

Matthew's siblings Joshua and Hannah have been sentenced to jail as accessories to murder. (9news)

The judge described Fisher's reasoning and actions as disturbing and callous.

"Having done the unthinkable, you were apparently not emotionally affected," Justice Hall said.

"You even tried to sell his car for your own benefit.

"It is also reprehensible that you chose to involve Joshua and Hannah."

Joshua was sentenced to four years while Hannah was handed three years and eight months.

But the judge acknowledged they had been presented with an "appalling dilemma".

He said "your father forced you to make a choice, he should never have put you in that position ... it was an appalling abrogation of parental behaviour".

Joshua was today sentenced to four years jail, with a minimum of two years.

Hannah was also jailed for three years and 8 months, but will be already eligible for parole at the end of this month, with time already served.

All three have been in custody since late October 2016.