Three sisters suddenly inherit a lucrative international business that trades in dreams of power, sex and glamour. So how will they all handle their extraordinary legacy?

It sounds like the plot of a Jackie Collins pool-side bestseller. But the truth is better than that, for this is the real inheritance of Collins’s three daughters, who are now planning the future of their late mother’s racy fictional characters while they prepare to celebrate her life and career with the release of a new documentary. Called Lady Boss: The Jackie Collins Story, it has unexpectedly delighted critics at the Tribeca film festival in New York this weekend.

The producers behind the Oscar and Bafta-winning film Searching for Sugar Man, which rediscovered a mysterious 1970s rock’n’roller, have come together again to chart Collins’s path to fame and fortune. And while this time the elusive subject of their film was hiding in plain sight, camouflaged in gold jewellery and leopard print, the revelations are just as surprising.

Collins, younger sister of film star Joan, sold 500 million copies of her 32 novels, each featuring ruthless, successful and beautiful women. Decades before her death in 2015, aged 77, she had established herself as a publishing phenomenon, punching almost book for book alongside the male airport fiction authors of the 1970s and 80s such as Sidney Sheldon and Harold Robbins.

To promote her fiction Collins also created an outlandish, shoulder-padded, mascara-wearing public image. This facade, the new documentary shows, was an effort, but it served as a reliable sales tool, as well as helping to preserve her different, quieter private life. Certainly Collins was no recluse – if you are married to American nightclub owner Oscar Lerman for 23 years then presumably some jetset socialising is part of the deal. Yet motherhood and female friendship were, it seems, much more important to her than would have sat easily with the raunchy, ambitious tenor of her stories.

British director Laurie Fairrie’s film charts the early life of the Collins sisters in London during the second world war and follows Jackie to Hollywood in 1956, where she attempted to join Joan as a hopeful film studio starlet. Just over a decade later, Jackie had turned away from the camera for good and written her first hit, The World is Full of Married Men. Her genre-defining novel Hollywood Wives came in 1984, with a hugely popular organised crime series, featuring Lucky Santangelo, running on until 2015.

The novels were credited with a kind of ballsy feminism in their day. Their emphasis on freedom, fun and sex meant that in an era of shaking off old prejudices, Collins’s sagas were almost as popular with gay male readers as they were with the women who devoured editions printed in 40 languages.

Reacting to the film’s premiere last week, American critics have hailed Fairrie for creating a page-turner of her own. Screen Daily praised the 90-minute documentary for providing “chapter-and-verse on a life of self-creation and steely determination”, while The Hollywood Reporter calls Lady Boss “engrossing and fast-paced”.

Collins’s three daughters, Tracy, Tiffany and Rory, all contribute on screen, as does sister Joan, who was often favoured by their father, showbusiness agent Joseph Collins. The film tells its story using not just excerpts from the books, but also from the author’s teenage journals. And it is these diary entries that have most impressed audiences, lifting the veil on a childhood dogged by self-doubt. In 1953 the younger Collins confided “I get an awful inferiority complex when I’m with Joan.”

An early eavesdropper, Jackie has admitted she used to hide inside the food trolley wheeled in for her father and his late-night card-playing guests so she could hear the way they all talked when no women were present. In later life she described herself as “a Bel Air anthropologist”, delineating the social mores of a world of deals, deceptions and divorces.

Dodging the blitz, the Collins family left London a number of times. Heading first for seaside towns such as Bognor Regis, Chichester and Brighton, they went on to Norfolk and Devon, the girls briefly enrolling in a string of schools. In her autobiography Joan has recalled the bond the family forged after the death of their mother Elsa from cancer in 1962. The young starlet stayed on with her father in his flat, but their 15-year-old brother, Bill, moved in with Jackie who became “like a second mother to him”.

Speaking in the new documentary Joan explains that the relationship with her sister, a subject of frequent speculation for Collins-watchers down the years, was always close but, like a marriage, “everything doesn’t go perfectly wonderfully all the time”.

The bestselling author was able to lend a helping hand to her glamorous sister once prospective film projects began to look a little uninspiring in the 1970s. Joan was cast as Fontaine Khaled, the disco-owning vamp at the centre of Jackie’s book The Stud. The sisters pulled off the trick again with the screen adaptation of The Bitch, effectively reviving Joan’s film career and putting her in line for her most triumphant venture, appearing as Alexis Colby in the long-running American soap opera Dynasty. However, tensions between the siblings apparently flared when Joan decided to write a few novels of her own in the 1980s. (No publishing slouch either, Dame Joan has sold 40 million copies so far, and been translated into a paltry 30 languages.)

It was at a lunch at the Ritz Carlton in London in 2015 that Jackie finally told her big sister that she was gravely ill. She had hidden her breast cancer diagnosis from almost everyone. Days later on that visit, just before her death, she was still promoting her latest book on television, resolutely coiffed.

Collins had always admired the hard-boiled writing of American author Elmore Leonard. The impact of this new documentary, which is to go into British cinemas from 2 July before a BBC2 screening at the end of the summer, might well be summed up by one of Collins’s favourite Leonard quips about his own fiction. “My material looks like a movie. Then when the studio gets into it, they find out it’s not quite as simple as it looks.”

• This article was amended on 13 June 2021. The character played by Joan Collins in Dynasty was Alexis Colby, not Coleman.