The 15-year-olds from Papua New Guinea were joined from chest to navel, with their livers attached.
They were surgically separated at 16 days at the Royal Children's Hospital.
Their parents decided not to tell Eustocia and Eaustina they were conjoined, to give them as normal a childhood as possible, until their recent return to Melbourne.
Dad Henry Bosin explained: "We did not want them to be embarrassed by telling them they were not born 'normal' twins."
The stunned twins found out a fortnight ago when visiting their now retired surgeon, Alex Auldist, who showed them film of their life-changing surgery.
Eustocia said she wanted to give something back by becoming a nurse, while Eaustina hoped to teach.
Former Rotarian Barrie Cooper, who arranged for them to be flown to Australia for their surgery, saw them yesterday for the first time in eight years.
"It was very emotional. I was very deeply moved ... to see them as 15-year-old girls because when I first saw them, I didn't think they had a hope," Mr Cooper said.
PNG Rotary had paid for their education so far, but $30,000 was needed so they could finish school and go to university, Mr Cooper said.
Photo: Eaustina and Eusthocia celebrated their 15th birthday in May [Mike Keating]
Source: Melbourne Herald-Sun