Two New Zealand families are in mourning following the killings that claimed three lives, including that of a five-year-old girl, in southern Queensland and northern NSW.
New South Wales police say they are investigating whether the father of the girl took some form of poison before he gassed them both in a car.
Former Nelson man Anthony Way, 33, and Tania Simpson, 31, were found stabbed to death in Simpson's unit at Robina on the Gold Coast on Monday morning.
Simpson's daughter Kyla Rogers, 5, had been reported missing at the weekend, and her body was found with that of her father, Paul Anthony Rogers, from Hamilton, after both had apparently died from carbon monoxide poisoning.
Police say Rogers may have stabbed Way and Simpson as Kyla slept in another room and then taken her away in his station-wagon.
Kyla's 20-month-old brother Bronnson, earlier thought to have been abducted, was found safe, having spent Sunday night with his grandparents on the Gold Coast.
Way's family said in a statement they were devastated by the loss of their son and brother and asked for privacy.
Way, who was known by many of his friends as "Ant", grew up in Nelson, attending St Joseph's Primary School and Nelson College.
He left New Zealand eight years ago and had been working in Australia as a renderer.
"Ant was one of those charismatic guys with an X-factor who drew people to him. He had a sharp sense of humour and would give you the shirt off his back.
He was generous, positive and had the most captivating smile," his family said. He is survived by his parents and elder brother, who live in Nelson and Blenheim.
The family planned to hold a memorial service on the Gold Coast, followed by a funeral in Nelson.
The details of the Nelson service are yet to be finalised. Gold Coast Detective Acting Superintendent Tim Trezise said Rogers and Simpson had been separated for eight months.
Simpson moved out of the family home at Ormeau, which the couple had bought two years ago from her parents, to become a manager of the Robina unit complex. Until last month, Rogers had been living in the caravan park they owned together in Inverell.
The couple had been planning to marry prior to their separation.
"They had been making plans to marry. I understand wedding invitations had been sent out," Trezise said.
"They'd been together eight years, but unfortunately the relationship broke down prior to the wedding.
"In difficult circumstances like this, when we have a triple homicide and what we believe at this stage to be a suicide, it's not easy to explain exactly why this happened."
Trezise said evidence found at the unit yesterday indicated Kyla might have slept through the double killing.
"Kyla had gone to bed in the unit, but was missing come Monday morning," he said.
"There's some evidence at the scene which indicates that she was asleep in bed the whole time."
NSW Deputy Police Commissioner Ross Barnett said Kyla's death appeared to have happened after a dispute.
"The man (Paul Anthony Rogers) and (Kyla's mother) had been estranged for some time; they had been living apart," he told the ABC.
"(Kyla's mother) had moved up to the Gold Coast and started a new life for herself and sadly this series of events has unfolded unexpectedly, and it has just been a tragedy.
"The whole family has been simply torn apart - a 20-month little boy left without a mother or a father."
* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or SANE Helpline on 1800 18 SANE (7263).
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