A husband and wife who committed immigration fraud after he fathered twins with another woman have won their appeal against deportation.

Photo: 123RF

The couple, from South Africa, were accused of grooming the woman, who had moved in with them.

They later lied to immigration officers that they were still living together when they applied for residence.

But the Immigration and Protection Tribunal said it was in the best interests of the couple's three children and the man's twin sons, now aged two, that they be allowed to stay in New Zealand.

The family arrived in 2011 after the man got a job as a cabinet-maker in Christchurch.

The couple met a woman through a mutual friend two years later.

She told them she was being sexually, physically and emotionally abused by her parents and she moved in with them.

But her parents told Immigration New Zealand that the couple had groomed their daughter under the pretence of providing her with free board.

When interviewed both the man, aged 47, and his wife, 46, admitted having an intimate relationship with the woman, saying it had ended and she had moved out.

When she became pregnant by him for the second time, the first having ended in a miscarriage, her parents told immigration officers that their daughter was living with the husband.

In an email in 2015, he assured Immigration New Zealand that he and his wife were "still very happily married".

Immigration New Zealand subsequently conducted two site visits to the couple's home address and another at the woman's home, which convinced them the couple were in an exclusive, stable and genuine relationship and they got residence later that year.

But in June 2016, the woman's lawyer sent Immigration New Zealand a DNA test report which strongly suggested he was the biological father of the twins.

It also received a Family Court affidavit from the father stating that he and his wife "remain legally married although we separated in mid-2014 and are living apart".

The husband told the tribunal he and his wife only parted for a week in 2014 and 2015, and that he slept with the 31-year-old while fixing her new home. He claimed she got pregnant deliberately to separate him from his wife.

The man moved in with her when the twins were born until she moved back in with her parents and obtained a temporary protection order. He has limited visiting rights and is trying for shared care, saying he has concerns about what he says is her fragile mental health.

The tribunal ruled he had carried out a deliberate fraud.

"[He] had sufficient opportunity to provide Immigration New Zealand with the above information but he chose not to because it would have jeopardised his wife and children's residence application," the tribunal wrote in its decision.

"The tribunal finds that [he] engaged in a deliberate and concerted effort to deny Immigration New Zealand all the facts regarding his marriage and his former relationship."

The wife of 17 years said their children were well settled in New Zealand and she regards her twin stepsons as her own children.

The couple said it would be devastating for them to have to return to Cape Town, where they claimed they went into hiding after being told they had to give away half their joinery business and were threatened.

The tribunal said the couple's children were completely innocent of their parents' wrongdoing but if their parents were deported they would have to leave too.

The twins would be permanently separated from their father, stepmother and step-siblings.

"His decision to engage in a relationship with AA [the other woman], who he knew was emotionally vulnerable, does not reflect well on his moral character and judgement," the tribunal's decision said.

"However, the tribunal is satisfied that his relationship with AA has permanently come to an end and that, since mid-2016, he and his wife have been living together in a genuine and stable and exclusive relationship."

It ruled it would be unduly harsh for the family to be deported.