This 9/11 hero’s legacy is larger than the big screen.

The sons of an NYPD detective who was killed when he courageously charged into the World Trade Center on Sept. 11, 2001 are following in their father’s large footsteps — and a new movie documents their call to serve.

Opening in select theatres on Friday, “Twin Towers: Legacy” follows the story of the Vigiano men, who have continued the family’s tradition as first responders after losing their father, Joseph, and his firefighter brother, John, in the terror attacks 24 years ago.

“I’m very proud of my boys. They are trying to make the world a better, safer place,” Joseph’s widow Kathy Vigiano told The Post in a recent interview.

“I think the two oldest became cops to become closer to their father and to share in that part of his life,” said Vigiano, president of Survivors of the Shield, a nonprofit that supports families of fallen NYPD officers.

In the heart-wrenching trailer, sons Joseph, 33, Jimmy, 31, and John, 24, detail their brief memories with their father, the tragic day they lost him and the legacy that pushed the elder two to become NYPD officers just like their dad and the youngest to join the US military.

The Lionsgate documentary, narrated by actor Dennis Quaid, recounts the Vigianos’ history and is peppered with old home videos from the young family’s time before the tragedy.

The film is somewhat of a sequel to director Robert Port’s 2003 Academy Award-winning documentary short “Twin Towers,” which detailed the loss and bravery of brothers Joseph and John Vigiano on September 11.

“I wanted to honor Joe, who was a close personal friend,” said Port, who is also the film’s producer, calling the movie “a passion project.”

“I also wanted to tell the story of a unique family whose values are the best of this country,” Port told The Post.

“This is a story about the selfless men and women who make sacrifices every day to help and save people without recognition.”

Joseph and John Vigiano hailed from a 180-year lineage of first responders, with Jimmy saying in the new film that “as long as the Vigianos have been in this country, they have been firefighters.”

Joseph was the first to deviate and become a police officer, and he quickly rose up the ranks of the NYPD.

He was among the first NYPD officers to race into the World Trade Center complex as part of the department’s elite Emergency Service Unit after terrorists crashed two planes into the skyscrapers.

He was just 34 years old, and his boys were all under 10 — with the youngest, John, just 3 months old.

Despite undergoing a tremendous loss and suffering trauma, the boys never wavered in their determination to grow up and be like their heroic father.

“I had the expectation to grow up to my father’s legacy,” Joseph’s eldest — and his namesake — says in the film. He joined the NYPD’s ESU last year.

At a solemn 9/11 memorial service last year, middle brother Jimmy emphasized he wanted to be a cop since he could talk.

Mom Kathy, a former cop who met her husband while working in the 75th precinct, said watching back some of the footage made her “uncomfortable” — but believes her late husband would have “loved” the project.

“Before he died, he was working on a show about emergency services. He wanted to share the heroics of the emergency service unit,” she said.

“He was outgoing. He loved being a cop. He was proud of all that he accomplished in the police department.”

Their son Joe now sports his father’s shield number, 4511, while Jimmy carries on his mother’s number — and both even worked together last fall to save the life of a shooting victim who nearly bled out on a Brooklyn sidewalk in October.

The family legacy is nothing short of a “quintessential American story about heroes and their legacies,” said Port.

“When I look at Joe and Jimmy, I see their father, which is high praise,” he said. “I am so proud of the men they have become.”