A childless Victorian woman accused of killing a "vulnerable" mother in order to take her children allegedly preferred others to call her "mum" than by her first name.
Christine Lyons and Ronald Lyons, 47 and 45, are on trial in the Victorian Supreme Court, accused of murdering 39-year-old Samantha Kelly at Bendigo in 2016.
The trial has been told there is no dispute Christine Lyons' current lover Peter Arthur killed Ms Kelly by striking her to the head with a hammer six or seven times.
But prosecutors said the Lyons, who are not related, were part of an "agreement" that Ms Kelly - who attended special needs schools as a child and still received support as an adult - should go "on a permanent holiday".
It is alleged Christine Lyons had a "powerful desire" to have a family, but was infertile.
Ronald Lyons and Peter Arthur were "devoted" to Christine, and killed Ms Kelly to give the woman "what she desperately wanted", prosecutors say.
It is also claimed the Lyons attempted to murder the mother-of-four a few days before her death by feeding her a "cocktail" of drugs.
A woman who lived nearby gave evidence on Tuesday, stating she'd considered having a baby for the childless Christine.
"I remember Christine told me she suffered from cancer and she couldn't have children and she asked people to have a child for her but she was unsuccessful," Rebecca Stow told the court.
"At first I said I'd think about it and then my partner said he couldn't do it."
Ms Stow said she often referred to Christine as "mum" as the accused murderer didn't like being called by her real name.
Ms Stow said on January 26, 2016, she visited the house to discover Ms Kelly had "up and left".
She said Christine claimed Ms Kelly abandoned her children and that the Lyons and Arthur would become parents to at least two of them.
She also said Christine claimed that Ms Kelly had broken into Christine's "egg bank" and stolen her eggs, and that the deceased woman's youngest children in fact belonged to Christine and the men.
A 16-year-old girl who lived with the trio told police the Lyons gave her "love" and she called Christine "mum".
"I never had a mum in my life or a dad figure ... I loved them as parents," the girl told police in a recorded interview played to the court on Tuesday.
"They gave me love, and that's why I lived there."
The trial continues.