Chris Dawson's murder trial has heard his second wife "had a motive" to kill his first spouse, Lynette, and that she once allegedly threatened to "get rid" of her.
Mr Dawson's identical twin brother Paul has been giving evidence on Thursday.
The siblings both played professional rugby league, worked as high school teachers and lived on Gilwinga Drive in Bayview in January 1982 when Ms Dawson disappeared.
There have been no verified sightings of her since.
Chris Dawson is accused of murdering his first wife in order to pursue an "unfettered relationship" with a woman known as JC, who was the family babysitter and a student at the high school where he taught.
He denies any involvement in Ms Dawson's disappearance and claims she left their home of her own accord.
Paul Dawson on Thursday told the court about a conversation he had with a family friend, Elva McBay, in mid-1981 that related to an incident at a fourth birthday party held for Chris and Lynette's daughter.
Paul said Ms McBay told him that she had been in the kitchen washing up when Lynette Dawson walked in looking upset.
"Elva said 'Lyn, what's wrong?' and Lyn said JC just said to her that if she got in her way, she'd get rid of her," he said.
The language is similar to that allegedly used by Ms Dawson in a discussion with her colleague Annette Leary shortly before she went missing.
Ms Leary last month testified that Ms Dawson told her Chris Dawson had "gripped her throat" in an elevator on the way to a marriage counselling session and said "'if this doesn't work, I'm getting rid of you".
An intercepted phone conversation between Chris and Paul Dawson was played for the court on Thursday.
It took place in 1999, after Paul Dawson had been interviewed by police about Ms Dawson's disappearance.
In the conversation, Paul can be heard saying to his brother, "if anyone had a motive, [JC] had more motive".
Paul told the court that in the 17 years he knew Chris and Lynette as a couple, he never witnessed any disrespectful behaviour.
"Chris thought she was beautiful from the start, and I never heard him say one derogatory thing about Lyn in 17 years," he said.
The trial has previously heard evidence from Ms Dawson's colleagues that she had turned up to work with bruises on her body.
JC was 'cruel' to Chris and Lynette's daughters
Chris Dawson and JC were married in 1984 and in the six years following lived on the Gold Coast near Paul and his wife Marilyn.
Chris and Lynette's daughters lived in the house too, and in 1985 JC gave birth to a daughter.
In his testimony, Paul said while Chris treated all three children equally, JC displayed favouritism towards her own daughter and was "cruel" to Chris and Lynette's two children.
"She refused to use the word 'family' unless she was referring to Chris, herself and [her daughter]," he told the court.
"She made [Chris and Lynette's daughters] put their laundry in a different basket .. they had to get out of the pool if [her daughter] wanted to go in."
He said on weekdays, JC would take her daughter to the Dreamworld theme park and refuse to pick up the other children from school.
"The girls were next door at the primary school but [JC] wouldn't drive them home, they would have to wait there until Chris or Marilyn came to pick them up," Paul said.
He said when JC brushed the hair of the two girls she would "pull it so tight their scalps would bleed".
"She really treated them like outcasts in their own home," he said.
JC has previously told the court Chris Dawson would not allow her to discipline the two elder sisters.
"I was only allowed to treat them like little princesses," she said.
"If I did discipline them, he would discipline me, and they came to see that I really had no authority."
She conceded that she probably didn't pay the girls as much attention as she did her own.
"I was consumed by my own child and the love I felt for her," she said.
The trial continues.
