We were impressed by Flo & Joan last year, with their show putting a mildly deranged smile on the face of musical double acts. We caught up with the duo, also known as the sisters Nicola and Rosie Dempsey, to hear how they balance a comedy career and a sibling rivalry.

What one thing do you remember most about how you met each other?

Nicola: It's not a memory I can personally remember, but photos show that the day Rosie was born I was so baby-stressed that I was bright, bright red and looked like I was about to have a nervous breakdown in every picture. Also when I was older I threw one of those Velcro bats at her head and it got stuck and had to be cut out of her hair.

Rosie: I was a fresh-out-the-sack baby so I don't remember our first meeting but apparently Nicola cried because she didn't like it. She was already nervous about me being the over-achiever.

What's the best thing about working with the other one?

Nicola: I love being the one who is right all the time.

Rosie: I love being the one who is right all the time.

What's the worst thing about working with the other one?

Nicola: Rosie believes she is right all the time.

Rosie: It's very tiring having to prove Nicola wrong all the time.

If your comedy partner hadn't become part of a double act, what do you think she would have done with her life?

Nicola: She would still publicly berate me, just not for money. And she'd continue to work in a butchers shop, which she loves probably more than doing Flo & Joan.

Rosie: She would have hidden in rural Canadian forest-land for as long as possible, then make a surprise return one Christmas with all her raccoon children like an episode of Eastenders. I think she would make a good newspaper features writer but she has a habit of choosing not to do things that people tell her to do. Failing all this, she would've stayed working on a deli counter.

If your current comedy partner was suddenly unable to work with you ever again, which famed comedian would you headhunt to replace them?

Nicola: Well I would need a partner with charisma and likeability, who can talk and pick up some basic percussion skills, and who is blonde to balance out my brunettishness … Sally Phillips. What a legend.

Rosie: Julia Davis. If she said no, which seems likely, I'd take Mr Blobby. He can play the piano. He had a number one single.

Flo & Joan: Alive on Stage, Pleasance Courtyard, 4–26 Aug (not 11), 4pm, £11–£12 (£10–£11). Previews 1–3 Aug, £8.