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Anna and Lucy DeCinque, who both live in Perth with their partner Ben Byrne, say they do everything together, including shower and sleep in the same bed.
Now the twins have revealed they want to experience pregnancy together along with their shared lover.
Lucy said: "We want to experience pregnancy together, we want to do everything in life together, we'll die together, we'll grow old together."
"We will freeze our eggs at the same time, it will be a challenge but we just want to be the same."
The sisters often wear matching outfits and put in a lot of effort to look as identical as possible.
In the past, the sisters have had different boyfriends, but say they're happier sharing Ben with one another.
"Ben treats us equally and it's been equal from day one. There's no jealousy whatsoever.
"He gets double the love, double the attention so he's never complaining. Twinning and winning."
Ben is a non-identical twin.
While the sisters would both like to marry Ben, Australia law prevents polygamy.
Previously the twins, who have admitted undergoing surgery, told The Sun: "We knew some guys might think it was kinky to date twins and see us as a trophy, so we had to feel sure that Ben genuinely liked both of us before we agreed to meet him."