"I'm bossy and grumpy," says Nina Raine, "and he's very sunny and adorably laid-back. I'm the bitch, basically." Across the table, her younger brother Moses tries to protest. "It's true, Mo," Nina says firmly. "I am."
We are discussing the pleasures and pitfalls of working together as brother and sister. Nina is a playwright and director whose 2006 debut, Rabbit, saw her lauded as a writer to watch. She has since had several acclaimed productions, both as writer and director: her last play, Tribes, has been produced around the world since premiering at the Royal Court in 2010.
At 29, Moses is nine years younger than Nina and he also writes for the theatre: his first play, The Survival Handbook, got him shortlisted for the prestigious Verity Bargate award. By coincidence, his next piece, Shrieks of Laughter, had its premiere a few days before Nina's Rabbit.
Now, Nina is directing Moses's latest play, Donkey Heart, an intense family drama set in contemporary Moscow. They've worked together before, – they co-wrote the final episode of Mistresses, BBC1's guilty-pleasure series about four women's lives and loves – but this is the first time Nina has been at the helm of one of her brother's plays. They seem to get on remarkably well: they live together in Camberwell, south London, along with Nina's boyfriend and Moses's dog, and Moses can't think of a single downside of working together. Nina, however, admits she can be hard on her brother. "I can be critical," she says. "And the other day, in rehearsals, Mo was eating sweets behind me… " Moses makes a face. "She turned round and went – he puts on a grumpy voice – 'It's really distracting.'" Nina laughs. "I certainly wouldn't have said it like that to [playwright] Caryl Churchill."
Donkey Heart brings together three generations of a Russian family, living cheek by jowl in a cramped flat. Its key theme is surveillance, both remembered, with the KGB's Soviet-era activities still casting a long, crooked shadow, and current, with the younger children suspecting their father of infidelity.
It was inspired, Moses says, both by his and Nina's Muscovite relatives – their mother, the former Oxford don Ann Pasternak Slater, is a niece of novelist Boris Pasternak; their father is the poet and critic Craig Raine – and by a trip he made to Moscow in 2010. "You can understand Chekhov when you see the huge skyline," he says. "It goes on forever – it feels like there's no escape. I just thought, 'This is so like every Russian play you've ever seen. I'd really like to do something like this.'"
The next few months are busy for both. After Donkey Heart, Nina has a play to finish for the director Max Stafford-Clark. "I'm at the end of the first act now," she says. "I really need to decide who's shagging whom." Moses, meanwhile, is working on a film adaptation of an Ian McEwan short story. They'll then be writing together again – a BBC film, this time, about a school.
Their approaches to writing are very different – Nina spends a long time on research, while Moses prefers to dive right in – but they have a shared outlook that seems to oil the cogs of their working relationship. "We have some of the same humour, some of the same voices," Nina says. "We're drinking from the same well."
Donkey Heart is at the Old Red Lion theatre, London EC1, until 31 May; oldredliontheatre.co.uk