They claim that Takapuna Grammar conspired with Natapu's father Jack to secretly remove their nephew from their home "to preserve their chances of reaching the 1st XV final for the first time in years".
Cole Ponton, the boy's uncle, said the school knew that if he and his wife had been made aware of the plan for Natapu to leave their home, they would have intervened to ensure Jay's focus remained on education, not rugby.
"What happened to our family at the hands of TGS is repugnant," the Pontons said. "Their moral and ethical compass has been severely compromised by an unhealthy desire to be recognised as an elite rugby school."
The Pontons have complained to the Ministry of Education and met with the Human Rights Commission on Friday. They are expected to meet again as they pursue a case against the school.
The Ministry of Education did not respond to a Weekend Herald inquiry into the status of Ponton's complaint, but a staff member not authorised to speak on the record said it had been received and was being assessed.
The school denies any wrongdoing and said in the case of Natapu they only ever sought to act in the boy's best interests.
They are supported by the boy's parents. Jay Natapu's father Jack said they wanted their son moved out of his aunt's home because of a "family issue" and the school rugby community "rallied around" to find him another home in the area.
"We're his parents. At the end of the day it was our decision and it should have been respected," Natapu said. "The school did everything it could to support Jay."
Speaking from Melbourne, Jay Natapu backed his father's version of events, saying he moved out of his relatives' home because he "was uncomfortable with emails being sent to his father" by the Pontons.
"It had nothing to do with rugby at all," Jay Natapu said. "It was pretty much all a family [matter]."
The Pontons believe the school secretive actions were "sinister" and put their three children, also TGS students, in an impossible position.
Barron-Afeaki said in his view "the secrecy was completely unnecessary".
"To just get a letter from the principal saying 'another relative has been set up to be Jay's guardian for the remainder of his time here' is not appropriate."
The saga began in January 2017 when the Pontons moved from Australia to Auckland. Natapu joined the family with his Melbourne-based parents' blessing to complete his final two years of schooling. His dad said the family viewed the relocation as an "opportunity".
In June last year, however, the Pontons said they woke one Sunday morning to find Jay had packed his bags and was moving a few streets away to live with McNair.
Later that week, the Pontons received a letter from the school congratulating them on the job they had done with Natapu, explaining how he had "benefited academically and personally", that he had been elevated to prefect status but that he would no longer be living with them.
The Pontons said there had been plenty of time to notify them of any issues but instead the school had co-ordinated the move with Natapu's father, Jack, behind their backs.
"I was on the school rugby fundraising committee," Vaoiva Ponton said. "They knew me well enough to talk to me if there was any issue they felt needed addressing."
Jack Natapu said he had tried to confront the issue with his sister but claims all contact had been cut off, forcing him to come to New Zealand to resolve it.
Jack Natapu said a Year 14 was never on the cards. He said the fallout had "taken a toll" on his son and he subsequently returned to Melbourne where he is now part of the successful Storm set-up.
Vaoiva Ponton said she was "devastated" the issue had split the family and said in her view the way that school had acted was "very sinister and unprofessional".
"Obviously I'm devastated that this has split the family but the way the school acted was very sinister and unprofessional," Vaoiva Ponton said.
The Weekend Herald requested an interview with school principal Mary Nixon, which was denied. We instead posed several questions to the school in writing, most of which they didn't respond to saying they were "protecting the privacy of our students".
Nixon and board of trustees chairwoman Vivien Kirk said in a statement that portraying this as putting rugby ahead of student welfare would not be in the "interests of fairness and accuracy".
Nixon said the board of trustees had "thoroughly" investigated the Ponton's complaints and found the school had acted appropriately at all times. The Pontons also claimed that Takapuna Grammar allowed Natapu to put himself forward for Maori representative rugby knowing that he was not a Maori.
Unhappy with the findings of that investigation, the Pontons went directly to the other agencies.
"As legal guardians and loving blood relatives, we invested in my nephew's health, wellbeing and future prospects, which were diminished . . . all in the name of pursuing rugby finals success," Vaoiva Ponton said.
"It was motivated, we think, by greed," said Cole Ponton. "Jay had seen and heard about the other rugby 'imports' getting payments and free board from the school, and he and his father [Jack] wanted some of that action too."
Takapuna Grammar denies this is the case, as does Jack Natapu.
The Pontons said their three children were badly affected.
"They were extremely close to Jay. The boys all shared a room with him. They loved him as a brother," they said.
It felt like he had been "stolen" from them, say the parents.
Jay Natapu acknowledged the move had come at a cost for his cousins.
"It was hard on them," he said, "because we were so close."
Not able to face seeing him in the school environment without getting upset, they moved high schools shortly after.
Vaoiva Ponton said they were angry at the boy's father but "angrier at the school" who he believed had acted with a "lack of professionalism and integrity.
"It has destroyed our family," she said.
McNair would not comment on any specifics of the Ponton's claims.