Along roads of scarlet hibiscus and exuberant tropical foliage are the white churches of Samoa. On Sundays the choir, singing in pure harmony, rises up to the cathedral ceilings in one soaring voice of divinity.

Pene Pati, once a child in those churches, is now a commanding, magnetic presence on the world’s greatest gilded stages – a universe away from the tiny, impoverished South Pacific island of Upolu, where he was born. A tenor specialising in the lyrical repertoire and bel canto, he is booked out until 2029, from the Metropolitan Opera to La Scala to Royal Albert Hall. Last month he received the pinnacle of arts awards in France, the Chevalier de l’Ordre des Arts et Lettres – a medal, he joked in a subsequent interview, that he’d been wearing around the house, much to his wife’s disdain.

Pati’s journey from Upolu to the opera mainstage was not without obstacles, as is detailed in a moving new documentary, Tenor: My Name is Pati, which makes its premiere at Sydney film festival this weekend.

But transcending the highs and lows is the rich velvet voluptuousness of his seemingly effortless voice; a voice imbued with colour, expression and the warmth of the Pacific, and described often as being full of sunshine.

In the film, South African soprano Golda Schultz says of Pati, “this is a beast of talent”, and violinist and conductor Guilio d’Alessio calls him “one of the best singers of his generation already”. When the conductor Marc Minkowski first heard his voice, he thought: “This is a Pavarotti rebirth.”

As a young man, Pati was told again and again that island boys don’t sing opera. In the film, he remembers one singing coach telling him: “there are no Polynesian singers, no one has ever done it, it is not in your blood, you won’t make it.”

“It did hurt a lot of times when people said ‘this is not for you, you should stop, what are you doing?’,” Pati tells the Guardian. “I have still got the emails to prove it. But you can either turn away or you can try to prove them wrong.”

Pati is speaking to the Guardian from Zurich, where he has been proving them wrong by performing Mozart’s La Clemenza di Tito with Zurich Opera. He believes part of his success comes down to the emotion in his voice, which people can’t help but respond to.

“People can feel the pain you have on stage, they can hear the love you have on stage. I think people need to feel something.”

It was New Zealand that shaped Pati and his younger brother Amitai, who is now also an international tenor. Pati was born in Samoa in 1987 but his parents, both nurses, brought the family to south Auckland for a better life when he was three. But they struggled, and most of the money they earned was sent back to family.

“They were always busy with work,” Pati tells the Guardian. “I do remember going to school without any food. They would say ‘drink water’. But I didn’t feel poor at all. When you are all going through the same struggle, it doesn’t feel bad.”

From an early age all four kids would sing to the residents at the retirement home where their parents worked. For four hours every Friday night for 15 years, Pati stood with his siblings performing hymns, Pacific island and popular songs. “Often we were the last thing those people heard,” he says.

Pene Pati Sr could be a tough father. “There is a fine line between discipline and domestic violence,” his son Pene says in the film, in which the whole family return to the humble house in Samoa, and spend time at the family house in Auckland, going through old photo albums and reminiscing with their father. Here the great tenor still has to mow the lawn, wash dishes and cook.

There is no bitterness; everything he does is a love letter to the man whose name he has carried across the world. “I harbour no resentment towards him,” he tells the Guardian. “He was a young man trying to figure it out himself. He was just trying to have good kids.” Of talking openly about it in the film, he says, “I wanted him to see this and feel forgiven. I feel like he carried it for so long. And he always thought to himself, ‘Did I do the right thing?’”

In year nine, the brothers came to the attention of Aorere College music teacher Terence Maskell, when the strapping rugby team Pati played for was drafted into the chorus of a school production of HMS Pinafore. After that, Maskell wouldn’t let Pene or Amitai get out of piano lessons or choir. “Music came so easily to them; they weren’t the most diligent of students,” the teacher says in the film.

When Pati met his wife, Amina Edris, at a young artist program, she was the one who made the first move. “I was three times the size I am now,” he says. “When you are that big you think there is no way this beautiful, cute girl would be interested … She told me she never once thought about size. And that is how I knew straight away.”

When he recounts that story with her in the film, Edris asks: “How shallow do you think I am?”

Pati came relatively late to formal opera, partly because he put others first. In Samoan culture, he says, “everyone takes care of everyone. Service is a big part of the culture.”

After winning the NZ Aria award in 2009, he was invited by former tenor Dennis O’Neill to study at the Wales International Academy of Music in Cardiff. A year later, back in New Zealand, the brothers and their cousin, baritone Moses Mackay, formed the trio Sol3 Mio, intending to raise funds for the others to join him back in Cardiff. Sol3 Mio was an instant success, but they only made enough money to send three – and without warning them, Pati put his brother, his cousin and his girlfriend on the flight, and he stayed behind.

Pati lost funding as a result. “I couldn’t understand what was wrong with putting your family first and wanting them to succeed,” he says in the film. Later he would turn down a prestigious fellowship at the San Francisco Opera to stay with Sol3 Mio, who were on the precipice of serious success. But two years and several bestselling albums later, he turned up in San Francisco unannounced and auditioned again. It was a risky strategy, but it worked.

Amitai watched his brother struggling with his ingrained cultural humility. On the same Zoom call, from Paris, he tells the Guardian: “We would say ‘look you have to be doing this for yourself. Otherwise what’s the point? If not for yourself then who?’ We were all proud of him and we wanted him to be proud of himself.”

The brothers insist that there has never been any rivalry. “It’s tough being a tenor,” says Amitai, “because there are only limited jobs and there are thousands of singers. When you are brothers from the other side of the world you have to stick together and say ‘you’ve got this’, you have no other choice. We back each other up all the time because we are in the same boat trying to do the same thing.”

Still, the more successful they get, the lonelier it can be. In April and May, Pene was performing in Zurich and Germany, while his wife, Edris, was singing in New York at the Metropolitan Opera. Later this month she will be in France to perform Mozart’s Mass in C Minor; in June and July he is in Milan at La Scala for Lucia de Lammermoor.

They move from hotel to hotel, studying scores, protecting their voices, isolated and alone. “You have this incredible high of doing something that you work so hard at,” Pati says, “and then you go to the room all alone and you sit there and take off your makeup and costume, and you are suddenly in this quiet space. And then you just put on your shoes and walk home.”

He does it partly, he says, for “the rush of excitement” on the stage. “That is my home.” But more than anything he does it to “clear the path for the next lot of Pacific singers who want to chase the dream … without being mocked.”

• Tenor: My Name is Pati will be at the Sydney film festival on 6 and 8 June, with a cinematic release on 24 July. Pene Pati and Amina Edris will perform together in Manon at the Wellington Opera. The shows are already sold out