"I'm 20 weeks, so due mid-January," she said, during an appearance at the Forty Winks store in Fyshwick.
"It's a boy, another boy. So we've got four boys between us now."

Not that she was showing too much.

"I'm like, 'When am I going to pop?Is there a baby in there?'," she said, with a laugh.

Alisa has a four-year-old son and Lysandra has two sons, aged three and five. They run their own interior design business in Adelaide and are busy with other business collaborations. Alisa did concede she had concerns about how she would juggle it all.

"I'm a little bit anxious about it," she said. "I'm so flat-chat now, throw a newborn baby into the mix which completely needs your attention ...Of course I'm anxious about it but you just make it work, don't you?"

The twins have designed a four-piece, limited-edition bedroom suite for Forty Winks called Asta which is Scandinavian-inspired, with Canberra fans the first to meet the twins during their tour of stores around the country.

"When Lysandra and I were designing this suite we thought about the difficulties we had finding bedroom furniture and we wanted to make it versatile," Alisa said.

"You can make it coastal, you can make it Scandinavian you could probably even make it country if you wanted to. And we wanted to combine different textures so you've got the natural elements of the timber and the softness of the fabric as well."

Anyone who's a fan of The Block knows that pillow placement and pillow numbers are crucial and the twins did spend quite some time arranging theirs in the Fyshwick store display.

"Dressing a bed is important. It's just the icing on the cake, isn't it?" Alisa said. "It's that extra 10 per cent that makes that difference and that wow factor when you walk in a room. You want to jump in the bed, it just makes it more inviting."

The former police officers have won $1.011 million across two series of The Block, first appearing in the 2013 series, which they won.

"It has changed our lives," Lysandra said.

"Sometimes you feel so fresh at it but then you realise, 'This has been our lives for almost three years.' We've been working on so much that people don't see and I guess all that hard work has paid off and after three years we're still able to be doing what we love."

The next series of the top-rating renovation show starts on WIN Television on Sunday.

"We always tune in," Alisa said.

"Sometimes it gets a little bit, 'Oh, I'm feeling the stress'. And it all comes back to you. But we've watched every series since."

Lysandra says she had to "pinch herself" that she and her sister had designed furniture for Forty Winks - in this case a bed, tall boy and bedside tables.

"We're really happy and proud of it," she said. "It was a long process but an interesting one to see how an idea comes to life. That was certainly not the very first thing we came up with. I hope in the future we can keep designing furniture."

And there's no sign of them slowing down.

"Ultimately, our goal is just to take on great projects because it's one of those jobs that doesn't feel like a job," Alisa said. "We love what we're doing."