Mahon is due out of prison on July 29, having served nearly five years for stabbing Audrey's only son Dean (23) to death in May 2013 at Northern Cross, north Dublin.
Her only other child, daughter Amy (15), mysteriously disappeared on New Year's Day 2008 from the home the teen shared in Spain with the controversial couple.
Insiders have also revealed that the pair plan to got to a friend's house in Wexford for a few days immediately after Mahon's release, before moving in together into the one-bedroom semi-detached council bungalow.
The couple also have plans to eventually move back to Spain, where Mahon is believed to own a house in the hills near Fuengirola.
Audrey previously said Mahon was "forgiven but not forgotten" for killing her son and has amazingly stood by him, even marrying him a year after the killing.
Sunday World tried to question her about her plans this week, she slammed the door, declaring "no, sorry, no".
The Dubliner, who shares her home with two pet Jack Russell terrier dogs, appears to be getting the house ready for Mahon's arrival as she had a man mow her front lawn on Thursday.
One local says Audrey generally keeps herself to herself.
But he admits people will be wary of Mahon, who was caged in 2016.
"People will be afraid of him," he said.
An elderly couple reacted in shock when told Mahon was planning to live amongst them in the house Audrey moved into three and a half years ago.
A middle-aged man nearby was more sympathetic to Audrey.
"We heard he's getting out," he pointed out. "She keeps herself to herself and best of luck to her."
While Audrey has plans to go to Wexford with Mahon and then move him into her home, she has said recently that she plans to go to Spain next April to mark what would have been Amy's 30th birthday.
She and Mahon moved to the west of Ireland town shortly after Dean's death, where they lived in a flat near the centre of the town.
During his trial, Mahon tried to claim that Dean was suicidal and plunged the knife into his own body during a fight over a water bottle - but the jury rejected the evidence.
Audrey has remained loyal to Mahon despite him stabbing her son to death.
Mahon was diagnosed with cancer of the throat and nose in early 2018.
She previously recalled the moment Mahon told her of his cancer news.
"He just said 'It's cancer', that's all he said to me and like that I just stopped in the middle of the street and started crying."
"He just said 'Stop crying, it's going to be ok'. All I said was what the hell else can happen to us?" she said.
She has occasionally visited her husband in jail, sometimes accompanied by his father.
Tragic teenager Amy went missing on New Year's Eve 2008 after leaving a friend's house in Mijas Costa, on the Costa del Sol, to walk back to her home.
She had lived in Spain with her mother, Mahon and younger brother Dean.
Audrey Fitzpatrick had left the family home in Clare Hall, Dublin, to be with Mahon, then a well-off estate agent on the Malaga coast, taking Amy and Dean with her.
Dean and Amy's heartbroken father, Christopher Fitzpatrick, previously said that he is still devastated by the tragic fate of the two children he had with Audrey.
"I am devastated over the loss of my two children. Things will never be the same since Dave Mahon came into my children's lives," Mr Fitzpatrick said.
Christine Kenny, an aunt of Dean and Amy, continues to campaign for information about her niece's disappearance.
Ms Kenny is the sister of Christopher Fitzpatrick, Dean and Amy's father.
In an interview last December, Ms Kenny said that the family do not hold out hope that Amy is alive, but called on the Government to begin a cold-case review.
"We have had numerous protests outside the Dáil and handed in petitions to the Government," she said.
"This was an Irish child who went missing overseas, but the Government did nothing," she added.