Christine Lyons has been sentenced to 30 years in prison for the murder of Bendigo mother of four Samantha Kelly as part of a plan to take custody of her children.

Her cousin-in-law, Ronald Lyons, was sentenced to 12 years and six months for attempted murder and assisting with the murder.

Ms Kelly, 39, was beaten to death with a hammer by Christine Lyons’ former lover, Peter Arthur, who was jailed last year.

Supreme Court Justice Stephen Kaye said Christine Lyons was the “architect” of a “premeditated, calculated and planned” murder and was “involved in the administration of each stage”.

He described the killing of the “loving, caring and devoted mother” as “heartless and thoroughly evil”.

“Samantha was vulnerable and, for all intents and purposes, defenceless,” Justice Kaye said.

“You sought to rob an innocent woman of her children so you could take them as your own.”

The victim was reported missing in January 2016, and her body was found in bushland south-west of Bendigo the following month.

When she was killed Ms Kelly’s children were aged 11 months, four, five and six.

The judge said Ms Kelly’s elder three children were “struggling to come to terms with the fact she’s no longer a part of their lives”.

“The youngest child will never know her mother,” he said.

Victim’s brother criticises ‘ludicrous’ sentences

Christine Lyons, whose sentence also includes a component for attempted murder, will be eligible for parole in 23 years.

Ronald Lyons will serve a minimum of nine years behind bars.

Outside court, Samantha Kelly’s brother Michael, who with his partner now takes care of his sister’s four children, described the sentences as “ludicrous”.

“Knowing one of them will be out before the youngest baby actually turns 10 is very gut-wrenching,” Mr Kelly said.

“We’re not happy with that, because she’s got to go her whole life without her mother and this man gets to get out before she even gets to turn 10 years old.

“Definitely I think it should have been life behind bars.”

Mr Kelly’s partner, Danielle Stevenson, said Christine Lyons did not care who she hurt in the process of pursuing her goal of taking custody of Ms Kelly’s children.

“At the end of the day, no amount of sentence is going to justify what happened in our life,” she said.

Christine Lyons changed children’s names

During the trial, the court heard Christine Lyons had an obsession with having children but could not bear her own.

The trial was told she had approached 10 people to ask them to have a baby for her, but none had agreed.

She so desperately wanted to be a mother that she killed Ms Kelly to take custody of her four children, and the two men were so devoted to Christine Lyons they wanted to help her fulfil her wish, the trial heard.

The four people lived together at a property in the Bendigo suburb of Kangaroo Flat. Ms Kelly lived in a backyard bungalow, but her children were living in the main house.

Christine Lyons was calling the children by different names.

The trial was told Christine Lyons had spoken multiple times to her housemates about drugging Ms Kelly and wanting her to take a “permanent holiday”.

After Ms Kelly’s death, the trio agreed to tell people Ms Kelly had told her children she’d had enough and no longer wished to care for them, the court heard.

They also agreed to say she had developed a drug problem, the jury heard.

Christine Lyons’ lawyer told a plea hearing earlier this month that her obsession with having children came from being “parentified” from a young age and being forced to care for her younger siblings.

The lawyer argued her intellectual disability and difficult upbringing lessened her moral culpability.

“While the jury found Christine Lyons was complicit, she didn’t strike the fatal blow,” he said.

Ronald Lyons’ lawyer told the same hearing his client maintained he was innocent of the charge of attempted murder.

“He’s not a sophisticated man. He’s a man who has a difficult background,” the lawyer said.

In February, Arthur had a further five years added to his 16-year sentence after a successful appeal by prosecutors.

-ABC