The babies, born on May 9, will be operated on at Singapore General Hospital in the fourth attempt in the world at such a separation, The Straits Times said.
The girls arrived here about a month ago with their parents, identified as Bhushan K.C. and Sandhya Shrestha K.C., and their grandfather.
The surgery is planned for the end of December.
The parents, from a mountain province, arrived with only two sets of clothing each and almost no money, the newspaper reported. They are being looked after by the Gurkha community here.
Prior to the operation, doctors said enough skin must grow to cover the heads after the surgery. The twins will be in the hospital for about three months.
Twins attached at the head occur only once in 2 million births.
"It is believed that the Nepalese neurosurgeon in charge, U. Devkota of Bir Hospital in Kathmandu, recommended Singapore" over hospitals in the United States because SGH had previously treated Napalese with complicated problems," the report said.
The most recent similar surgery was performed in South Africa by John Hopkins surgeons in 1998. Both twins are alive.
(la/dpa)