Conjoined twin girls from Bhutan are due to undergo landmark separation surgery in Melbourne this week.

Fourteen-month-old Nima and Dawa are joined at the torso, but surgeons at the Royal Children's Hospital plan to offer them independence after a marathon procedure scheduled for Friday.

"We feel we are in a position to give mum her ultimate wish which is to go forward with the separation of the children," pediatric head surgeon Joe Crameri told reporters on Tuesday.

After extensive tests and scans to ensure the girls' nutrition, the surgical team is confident about the operation.

"We've been able to review some sophisticated scans that have been done ... in simple terms the plumbing certainly looks favourable to us," Mr Crameri said.

"Certainly we feel it gives us the opportunity to separate the twins and to preserve good function for both girls."

The girls share a liver and they are believed to share part of a bowel but the extent of their combined functions will not be known until the surgery is underway.

"The imaging seems to be favourable in terms of what we need to achieve but surgery is always a case of 'expect the unexpected' and certainly that will be the case here," surgeon Tom Clarnette said.

The liver specialist added that the procedure could take six to 12 hours and the rick of complications was real.

"Getting the separation is going to involve getting the liver divided safely and there's a blood-loss potential there," Mr Clarnette said.

The surgery and recovery are estimated to cost at least $350,000.

The state government pledged to cover surgical costs, with other funds raised to go towards the girls' Australian rehabilitation and return to Bhutan.