Fazli Rahim, 42, and 31-year-old Saima Gul, were jailed for life and told to serve at least 23 years for murdering Mohammed Noor at a flat in Pollok, Glasgow, in May 2012 in what the judge Michael O'Grady, QC, described as one of the most appalling crimes he had encountered.
The brutal attack was witnessed by a 12-year-old girl who told how the two attackers sent her to the kitchen of the flat for a knife, then ordered her to get a bigger blade. She was also made to bring a hammer used in the incident.
It was claimed in court that Gul, who was 16 when she entered into an arranged marriage in Pakistan, was forced to live with the murder victim Mohammed Noor in a "dishonourable way" which led to her being abused after her husband Rahim had entered a bigamous marriage.
At the Court of Criminal Appeal in Edinburgh, Lord Drummond Young ruled the sentences were too severe, saying one of the relevant factors was that not enough weight was given to "cultural factors" in the case.
Rahim had his sentence cut by four years and can now apply for parole after 19 years and Gul had her sentence slashed by six years and can apply after 17 years.
The court heard Rahim moved from the North West Frontier Province to Glasgow nine years after the marriage with Gul, which was arranged by their parents.
Gul was pregnant when she remained with Rahim's family, while he used false documents to travel to the UK to look for work.
By the time she joined her husband in 2008, Rahim had fathered four children after a bigamous marriage to a Scottish woman.
A ruling reveals it was submitted on Gul's behalf that "cultural differences existed between the UK and the society from which both appellants and the deceased came" and she was required to live with the deceased "in a dishonourable way".
Gul, who had a child by Mr Noor, had claimed he had raped and abused her and that he beat her with his hands and with wire.
Her representative said she broke with cultural norms to go to a police station the day before the murder to complain that Mr Noor had been harassing her and was keeping her child prisoner in his flat.
Officers escorted her home and told Mr Noor to stay away from her. The judge said he was "extremely sceptical" about the claim this had led to the fatal confrontation.
Lord Drummond Young said: "We accept the appellants came from a society which in many respects is very different culturally from the United Kingdom.
"The history of the relationship of the two appellants and of their relationship with the deceased is highly unusual, but the trial judge did not attach any significant weight to this. This may have been because of the absence of clarity about what actually happened at the time of the killing. Nevertheless, we think some weight should be given to cultural factors."
He said he believed the judge also attached "too much significance" to the absence of emotion of the couple during the trial.
Lord Drummond Young said that, while allegations Gul had been abused physically and sexually by the deceased were "very unsatisfactory", the fact she became pregnant by Mr Noor "lends some some support to this suggestion".
The appeal court judge also said the aggravating features of hamesucken - a premeditated home break-in with a view to violence - and the vulnerability of the deceased were absent.
A jury previously heard 22 days of evidence and speeches, then rejected Rahim's claim he was merely a spectator while Gul carried out the fatal attack.
They also rejected Gul's story that Mr Noor had tried to rape her and her husband had intervened.