The troubled pair are the subject of Tête-bêche, a film directed by 20-year journalist Luther Ng which premiered on Friday at the Hong Kong Arts Centre.

The title refers to a joined pair of stamps in which one is upside-down in relation to the other, produced either intentionally or accidentally.

The siblings find their lifelong beliefs challenged as they begin to explore each other’s lives. It leaves both their world view and their relationship broken, while their father looks on, powerless to help.

Ng, now in his late 40s, refinanced his home to raise money to make the movie with two other journalists. For him, the characters in the film are like the stamps – living in opposite worlds but inextricably linked, bonded by blood.

“After Occupy, we felt lost,” Ng said. “It was like some of our long-held values – transparency, democracy, openness and peace – were all gone, and society had changed.

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“After being in journalism for one to two decades, the three of us have all reached middle age, so we decided to pause and take a rest. That was when we decided to make this film. We wanted to see what had happened to society.”

Hong Kong’s police force was widely criticised for what many saw as a heavy-handed approach in dealing with the 79-day mass sit-ins in 2014 that left sections of the city at a standstill.

Accusations were levelled that officers beat up demonstrators and collaborated with gangsters.

After the movement dissipated, having achieved little towards its aim of securing democratic reforms in Hong Kong, some protesters became increasingly radicalised. Eighteen months later clashes broke out in Mong Kok between police and protesters, who used bricks and water bottles to attack officers.

Ng’s team began filming in 2016 and completed the final edit just a few days before Friday’s screening. They interviewed 83 protesters, police officers and journalists who were part of Occupy, as they searched for inspiration for the film.

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“During our research we found similar problems in real families,” Ng said. “A girl told us her father, a police officer who was usually gentle, would become seriously cranky when he saw Joshua Wong Chi-fung on television. She said she did not know how to live with her father any more.”

Wong was a key student leader of the Occupy movement.

“But our inspiration really came when we found a pro-democracy student leader whose father was a photojournalist and brother a police officer,” Ng said, referring to the protagonists.

One scene depicts Occupy protesters confronting police who have turned a blind eye to gangsters stirring up trouble in the crowds.

“There was no script for the actors and actresses in this scene – they were free to improvise,” Ng said. “Many of them were students at film school. When the cameras stopped rolling, those playing protesters were in such real anger and were still surrounding the actors playing police officers. We even had to separate them.”

Ng adds: “There is no moral to the film. The ending is open. We hope the film will encourage viewers to reflect on our torn society.”