The twins, who were delivered by C-section, flew to Australia last month for the surgery that would finally divide them.
Surgeons at Melbourne's Royal Children's Hospital are confident the operation will go ahead today, with the 15-month-old girls thought to be strong enough for the six-hour procedure.
Crameri said if there were any unexpected problems during the operation, the hospital had all the resources and experts on hand that it would need. The bowel is known to be mixed, but Crameri said doctors don't yet know if the girls have separate bowels sitting next to one another or if the organ is shared between them.
According to Herald Sun, a newspaper based in Melbourne, Nima and Dawa would be taken for surgery after 8am (Melbourne time) on Novermber 9, where they will be known as Green and Red to avoid mix ups.
As well as the issues with mobility and comfort, Lodge said the twins had recently been losing weight, which had been a concern to doctors who are now observing them closely.
"There weren't any things inside the girls' tummies that we weren't really prepared for", he said.
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Doctors at the Royal Children's Hospital in Melbourne had hoped the procedure would be straightforward, but said it would be impossible to know until the procedure began.
Zangmo would spend the day praying and meditating, she added.
"There will be challenges over the next 24 to 48 hours as with any surgery", Dr Crameri said.
The sisters were brought to Australia with their mother Bhumchu Zangmo in October and have been staying at the Children First Foundation retreat in Kilmore.
The Victorian government has offered to pay for the procedure and recovery, expected to cost at least A$350,000 (US$254,740).
Bhutan is a poor Himalayan kingdom where doctors did not have the expertise to separate the girls, who were joined from the chest to the waist.
The twins are expected to head home with their mother once they've recovered.