A statement by Greg Simms was read out in the NSW Supreme Court, describing how the loss of his sister had impacted generations.
"We considered you an equal in all respects. We trusted you. You repaid us by committing the ultimate betrayal," Mr Simms wrote of Dawson.
Thursday's sentencing hearing comes 10 weeks after Dawson, now 74, was found guilty of murdering his wife in January 1982 to have an unfettered relationship with one of his high school students, known as JC.
"It was a brazen act of a conniving monster hell bent on one thing, getting what you wanted at any cost," Mr Simms said.
Wearing prison greens sitting in the court dock, Dawson listened to statements from Mr Simms as well as Lynette's sister Patricia Jenkins and his own daughter Shanelle Dawson who was four years old when her mother was killed.
Before reading her statement, Shanelle paused to stare at Dawson across the courtroom, breaking into tears before speaking.
"The night you removed our mother from our lives was the night you destroyed my sense of safety and belonging in this world," she said.
Her life had been shattered, she found it difficult to trust men, and she had been diagnosed with PTSD after learning what her father was capable of, she said.
"The torture of not knowing what happened, or what you did with her body - please tell us where she is. I hope you will finally admit the truth," she said.
Ms Jenkins said she had been "confused, alarmed, distressed and in a deep dark void" upon hearing of her sister's disappearance.
Dawson would lie to his daughters after the murder, telling them that Lynette wasn't their "real mother" but was only pretend because she had walked out, Ms Jenkins said.
"Lyn's disappearance and the journey has since taught me that no one is safe from tragedy. It can unexpectedly strike anywhere and justice can also be a long time coming."
Mrs Dawson went missing from the couple's Bayview home in Sydney's northern beaches when she was 33. Her body has never been found.
JC, who was also the family babysitter, was installed in the Bayview home as Dawson's partner days after he killed his wife.
Also on Thursday, crown prosecutor Craig Everson SC said Dawson had planned a "deliberate and conscious act" of domestic violence with an intention to kill.
He said a crime of "very great heinousness" required a term of life imprisonment.
In this case, Dawson's crime was heinous because of the significant harm to others, delays in the case and the ex-rugby player's lack of remorse, Mr Everson said.
Dawson's lawyer Greg Walsh disputed claims the crime was at the high end in terms of objective seriousness.
"This is not a case of such heinousness that it comes within the worst category of cases," he told the court.
He said Dawson had suffered under the "most constant and egregious publicity" for four decades.
His health was also deteriorating, with Dawson showing signs of chronic traumatic encephalopathy, a brain condition often experienced by those who play contact sports.
Dawson required extra protection while in custody, being threatened and taunted "day in, day out, minute after minute, hour after hour" by the name, The Teacher's Pet, Mr Walsh said.
The Teacher's Pet podcast by The Australian's Hedley Thomas shot the case into the public eye, garnering millions of views across the globe.
Dawson has already filed an appeal against his conviction.
Outside court, Mr Walsh told reporters that if this appeal failed, Dawson would die in jail.
Mr Simms, when asked whether he thought Dawson should perish behind bars, told reporters that his brother-in-law should do his time and again urged him to reveal where his sister's body was.
Justice Ian Harrison will deliver the sentence on December 2.
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