In the 1940s, scientist Bertold Wiesner and his wife, Mary Barton, set up a fertility clinic in London. In 2012, it was revealed the couple had used Wiesner’s sperm to impregnate their clients. By some estimates, he has up to 600 biological children.

More recently, an American woman’s search for her roots yielded nine siblings. Her father – a fertility doctor – allegedly told patients he had used the semen of medical students. In fact, it was his own.

Then there’s the American doctor accused of a similar crime. And a Dutch specialist. And an unlicensed British donor, who believes he has 800 offspring. “I’d like to crack 1000,” he told the BBC.

These extraordinary stories caught the attention of award-winning writer and producer Imogen Banks. She and her colleagues – including Jonathan Gavin, Michael Lucas and Benjamin Law – were contemplating a drama about people trying to conceive through IVF. “But suddenly, we started seeing these cases from overseas,” Banks says. “We went, ‘This is really a story about family and what it is.’ It’s about nature versus nurture. How your identity is constructed – and what happens when a central pillar of your identity is suddenly removed.”

In this moment, Sisters was born. Beginning on Wednesday on Channel Ten, it stars three thirtysomething women who discover they’re related: dutiful daughter Julia (Maria Angelico), troubled children’s entertainer Roxy (Lucy Durack) and corporate lawyer Edie (Antonia Prebble).

The story begins with a death-bed confession from IVF pioneer Julius Bechly, who admits to The Age he provided much of his clinic’s “anonymous” donor sperm. Problem is, he doesn’t die. It’s left to Julia – who believed she was his only child – to pick up the pieces. So begins the daunting task of finding her siblings.

Magda Szubanski plays Diane, Roxy’s mother and manager. On a warm spring day in Melbourne’s north, she films a scene outside her character’s house: a triple-fronted, 1960s, orange brick home.

“Where did you get that?” Diane snaps at husband Ron, played by Roy Billing. It seems Roxy has fixed him an expired cup of soup. “It must be about eight years old!”

Of course, Ron’s snack isn’t the real reason for Diane’s anger. Like many Catholic women, she wasn’t taught how to recognise – or assert – her needs. She finds it easier to vent her frustrations over small domestic matters.

“It’s that Catholic thing of, ‘Everyone must have the same amount of cordial; no one can have more than anyone else,'” Szubanski says. “When it manifests as social justice, it’s beautiful. But there’s also a kind of flattening aspect to it. Maybe that’s why [some Catholics] grow up to become celebrities.”

Reflecting on her own Catholic upbringing, she laughs. “You get taught, ‘Don’t flaunt your wares.’ It took me a long time to throw that off; to learn that my job requires me to be a show-off.”

Szubanski’s superb memoir, Reckoning, illustrates why she was drawn to Sisters – a story about family, identity and the search for meaning.

You don’t want to make the trauma your identity …

Magda Szubanski

Her Polish father, Zbigniew, fought Nazis as an assassin in the Second World War. The terrors he faced are unimaginable; his acts of bravery even more so.

Beneath the humour of her Scottish mother, Margaret, she sensed a “querulous hypervigilance … a child full of panicky uncertainty”. Which is no surprise after viewing Szubanski’s episode of Who Do You Think You Are, the SBS genealogy program. During filming, she learned her maternal grandfather, Luke, was born into dire poverty. Ten of his 13 siblings died in childhood. After fighting in the war, he was tormented by shell shock.

“Trauma is one of those things that is much better understood now: the way it plays out over generations, how things from the past can affect you,” she says. “You don’t want to make the trauma your identity – but you do need to understand it. That’s the idea I wanted to give expression to in the book.”

Our interview occurs barely a fortnight after her mother’s death. Szubanski would love a break, yet she is committed to fighting for marriage equality. “These things never happen at a convenient time. I will look after myself – but I can’t just dip out. I absolutely know my mother would have wanted me to do this.”

Coming out on live television, in 2012, changed her life. “The act of doing something brave is what makes you brave,” she says. “I learned that from my Dad. You don’t sit around waiting for the feeling to strike.”

Sometimes, fans tell Szubanski how similar their lives are. She likes to rib them: “I’m the short, fat, lesbian daughter of an Irish-Scottish woman and a Polish assassin: how are we the same?” But she knows what they mean. “We all feel like outsiders. When you tell the truth about yourself, people relate to that.”

This is why Sharon Strzelecki became one of our most beloved comic characters. “Australians like her not just because she’s funny, but because she’s poignant. They really feel her vulnerability.”

Durack understands. Years ago, she moved from Perth to Sydney for the stage musical, Mamma Mia! Homesick, she watched Kath & Kimon repeat to cheer herself up. “It brought me such joy and comfort,” she says. “Each time, I picked up something different.”

Having appeared with Szubanski in the 2013 film, Goddess, she leapt at the chance to work with her on Sisters. At first, Diane was slated to be Roxy’s unrelated manager. But when producers noticed their chemistry, they made Diane her mother, too. (The pair are now firm friends. Recently, Szubanski invited Sisters’ cast and crew to her house for a barbecue.)

“Roxy’s lived a very controlled life, and Magda is very much a stage mum,” she says. “That’s why Roxy is excited to learn about Julius. She latches on to it as the reason she’s so messed up.”

Accustomed to portraying “golden girls” on stage – including Glinda in Wicked and Elle Woods in Legally Blonde – Durack enjoys playing a flawed character. “What I love about these women is that they’ve all lived messed up lives, in their own way – but they’re all making an effort. And that leads to some very comic moments.”

This could describe the characters in Offspring. While both programs share certain writers and producers, however, there are major differences.

“Offspring has always had that slightly elevated tone, with all the fantasy and flashbacks and inner monologues,” Banks says. “Sistersis more earthed and naturalistic. It’s still funny but the humour comes from distortions; from the juxtaposition of each character’s response.”

Unlike other dramas, it does not inhabit a well ordered moral universe.

“I love that Julius is consistently unapologetic, because that’s what happens in life. You rarely get the satisfaction of people saying, ‘I’m sorry, I was wrong.’ You just have to get on with it.”

Gavin says: “We deliberately focused on characters at the cusp period of their 30s. That’s when you realise that you’re not just getting ready to live – you’re actually living your life right now. In Offspring, love was the answer to people’s problems. Whereas in Sisters, love is a complicating factor. Love can be confused or conflicted or sent in different directions. It’s not always healthy.

“It’s a great way to explore what family really is.”

WHAT: Sisters
WHEN: Ten, Wednesday October 25, 8.40pm

By Michael Lallo for The Sydney Morning Herald