They spent a lot of time just staring at each other when they met for the first time in Australia in July.
Trying to catch up on a lifetime in three weeks was hard for the "diblings", US-based Greg and Cassandra Hallberg, and Australians Fiona Darroch and her sister Allison. Neither Greg nor Allison wanted their surnames published.
But the shock of discovering their genetic heritage was overtaken by excitement of finding new blood relatives.
With them was Anne Crossey from Ireland who, through her own quest, had brought them together. Crossey was also conceived through a sperm donor at the Durban clinic run by Dr Norman "Tony" Walker, but tests showed he was not her biological father.
"I am really lucky to have wonderful new siblings," Greg told the Sunday Times. "I don't think we look alike, but Allison's daughter could easily be mistaken for mine."
Hallberg said she did not really know what to expect.
"I mean, what does it really mean to share 25% of your DNA with someone?" she asked.
"Part of me also felt like I was nuts for spending thousands of dollars and hopping on a plane to fly across the world to meet total strangers who could easily be axe murderers for all I knew. My co-workers had bets going if I would ever be seen again!"
Hallberg said it usually took her time to warm to people, but she felt instantly comfortable with Alison, who fetched her from the airport in Sydney. They soon discovered several things in common, like an allergy to nickel and a "major aversion to seafood".When she met Fiona she said she couldn't stop staring at her because she looked so much like her.
"And then, when I met one of her daughters, again I couldn't stop staring because she had the same expressions as my daughter. What really caught me by surprise was that we all shared a very similar quirky sense of humour. It was very comfortable, like we had always known each other despite the arguments over our totally different dialects of English [Australian English, Irish English, South African English and American English].
"The bottom line is I have no reason to grieve or hide this secret. No-one committed a crime here. I am really grateful to Tony Walker for giving me life and giving my parents the gift of a really great family. I hope to enjoy a close and meaningful relationship with my new-found sisters."She said she was concerned about Walker's children from his marriage to Molly.
"I worry deeply that Tony's daughters, my other half-sisters, may be embarrassed about what their dad did and I want them to have peace and know their dad gave us all a gift, albeit a bit of an unorthodox one."
Darroch said the diblings - and Crossey - were planning another get-together next year. "We get along very well," she said.
Crossey said: "It's funny how flexible you start to become about what constitutes family. But when we were in Australia I saw them looking at each other's faces . scanning for resemblances - an identification with the biological fact that they share a biological father. I want to have that. I want to meet someone who is my age and who I can look at and think: 'We share DNA, we are fundamentally connected.'
"We were the secret babies of the Durdoc Clinic and we're not a secret any more. It's been a lot for all of us to take in.
"We really want to get the conversation kick-started - our mothers are all 70 or 80 by now, so a lot of people are never going to find out. People will be taking these secrets to the grave if it isn't addressed.
"I think there used to be a great shame in male infertility, but times have changed and it's time to talk about it."..