CUDDLED in the arms of doting parents Mark and Matt, newborns Tate and Estelle are the contented faces of a unique Australian modern family.

Conceived from eggs harvested from a single donor woman, separately fertilised by the gay dads, implanted into two surrogate women in Thailand, the bubs were born an hour apart in a Bangkok hospital.

On Monday the proud parents Mark and Matt are expected to receive the miracle babies' Australian citizenship and are preparing to bring them home to Adelaide.

The dual boy-girl surrogacy delivered at virtually the same time by caesarean section to gay parents is believed to be an Australian first.

For Mark, 29, a university lecturer, and Matt, 29, a primary school teacher, who have been partners for more than a decade, the surrogate births have been an emotional journey costing around $80,000 - and worth every cent.

Commercial surrogacy, where the woman carrying the implanted foetus is paid, is illegal in Australia, and adoption by gay couples is not permitted in South Australia.

This left Mark and Matt to look overseas for the biological children they have always wanted.

Mark is Adelaide born and bred, Matt is originally from the state's Mid-North, and both intend to make Adelaide their long term home so moving to an area with different legislation was not an option.

They are confident their stable relationship, backed by family support and good jobs, will give their children a strong start to life.

The men had to wait outside the birthing rooms in Bangkok's BNH Hospital while the births took place, and had fleeting glimpses and only brief physical contact with their children immediately afterwards until it was time to take them home.

"At that moment, as we got into the taxi, it was real," Mark said, speaking from their apartment in Bangkok's financial district of Silom, which has been their home since Boxing Day.

"It had been exciting up until then but at that moment we knew we had our children."

Matt said: "That was the moment we knew Tate and Estelle were finally ours and no one could take them away."

The path to parenthood has taken years and many serious decisions.

The men had considered surrogacy in the past but a recent law change in India - where many Australians had turned to in the past - banning gay men from commercial surrogacy, and a desire to have children by their 30s, spurred them to action early last year.

Research including checking Facebook surrogacy groups pointed to Thailand as their best option.

An agent there arranged for an anonymous egg donor, offering a choice of ethnicities. The men chose caucasian.

Eggs were harvested in Thailand, checked for health then each man fertilised one of the eggs in a Bangkok IVF clinic.

They do not plan to reveal which of them fertilised which egg for the time being but eventually will tell the children as they grow which parent is their biological father.

"It is obvious to us that they are both our kids, that they are equally loved, and for the moment we are not going to tell the outside world which is related biologically to each of us," Matt said.

"It means all the grandparents will love them equally, and it sends a message that these are both our children.

"In time to come we will tell the kids but by then it will not be a big deal - we are just another family."

The men do not intend to contact the donor mother, although they have left the door open should Tate or Estelle be curious in later life.

"There will be no secrets from the children when they are old enough to understand," Matt said.

"We have decided we will not contact the donor but we do have photos of her which we will give to the children.

"Every family is different. I grew up with only a sister, and to me the idea of someone saying "where's my mother?" is like me saying "where is my brother?" - that is just not the family you are in."

After the eggs were harvested and fertilised at Bangkok's All IVF Clinic, they were implanted in two Thai women who were paid to carry them for the next nine months under a written contract.

Under Thai law the women must already have had children and also be single.

The first clause is to ease emotional bonds and also negate the risk of anguish should the woman be unable to have children later in life.

The latter exists because, if the surrogate is married, her Thai husband legally becomes the father.

Despite the enormous odds both IVF implants thrived, resulting in both being ready for the caesarean delivery on January 6.

Mark and Matt arrived in Thailand a week beforehand, anxiously awaiting the births.

Since then there have been various paperwork hurdles to clear from their temporary home in a Bangkok apartment

DNA tests had to be performed to confirm the South Australians are the biological fathers. Blood from heel pricks on the babies were taken in the Bangkok hospital with an Australian Embassy official present as a witness, and sent to an Australian laboratory which confirmed Mark and Matt as the fathers.

Then Embassy officials last week held a detailed interview with the two surrogates to ensure they were still voluntarily willing to carry out the contract and let the two fathers take over as sole parents.

The two fathers do not intend to stay in contact with the surrogates.

After the Embassy meeting the women were encouraged to hold the newborns and have photos taken with them to ensure they were willing to relinquish them.

With Australian citizenship for the children, the new family is waiting on fast track passports before finally leaving Bangkok this week to start a new life in a suddenly crowded house in Adelaide, now full of cots, toys and the paraphernalia of parenthood.

Both men are grateful for the full support of their parents, and each has an older sister with a son who are also delighted with the additions to the family.

Both also say they have not experienced discrimination as gay men and expect changing social circumstances will see acceptance of an unconventional family brimming with love.

"We have not had any negativity at all, in fact even strangers who learn about it have been supportive," Matt said.

"I think we live in a day and age where we don't face the setbacks people had to put up with not so long ago."

Mark noted any critics should simply look at the love surrounding the babies.

"We do have some expectation that people will be accepting of diversity," he said. "Some people may say irrational things but families are diverse."

Matt chimed in: "There is not a part of parenting that is gender specific."

* Mark and Matt asked that their surnames not be used. Their children will carry both surnames, hyphenated.