The teenager who could hold the key to the horror triple murder on an exclusive Cape Winelands estate is fighting for her life.

Her brother, the only other survivor of the crime, has been released into the care of an uncle after being taken in for questioning by police.

On Tuesday, the bodies of millionaire international businessman Martin van Breda, his wife, Teresa, and their son Rudi, 22, were found in their palatial home on the De Zalze Golf Estate in Stellenbosch.

Daughter Marli, 16, suffered extensive head injuries in the attack, while her brother Henri, 20, appeared to have suffered cuts and bruises.

Police are yet to make any arrests or give a possible motive for the shocking crime.

Paramedics who went to the Van Breda home on Tuesday confirmed that an axe had been found on the scene but police have yet to confirm this as the murder weapon. The axe has been sent for forensic testing.

Investigators say the crime scene is likely to be cleared only by tomorrow.

A family spokesman, Pretoria lawyer Don Bosman, said last night that Henri was staying with an uncle.

"I will be sitting down with the family tomorrow to sort out funeral arrangements," he said.

The spokesman for Vergelegen MediClinic in Somerset West, Carla Hanekom, said Marli had undergone surgery on Tuesday.

"She is critical, but stable. At the moment no one is allowed to see her, not even close family members," she said.

Pupils and teachers at Somerset College, where Marli is in Grade 11, attended a chapel service and several prayer sessions yesterday.

Peter Armitage of Anchor Capital, an asset management and investment company, worked closely with Martin and described him as a "great man and friend".

"He had such wonderful plans to change South Africa through education," Armitage said. "He had plans to start a chain of low-cost private schools, aimed at the lower-end market.

"Martin was an engineer and the founder of Netstar, which he sold to Altech in the mid-1990s. Then he started Woodhill College in Pretoria in 1999 and I think this is where he discovered his passion for education."

Van Breda later sold the college to the Curro group of private schools for R185-million and moved to Perth, Australia.

The family returned to South Africa about a year ago and moved into the exclusive golf estate in Stellenbosch, where the average house price is R9-million, according to estate manager Boet Grobler.

The chairman of the estate homeowners' association, Eben Potgieter, said on Tuesday that the security of the complex had not been breached.

Martin van Breda was a "master licence partner" of premium property company Engel and Völkers in Australia.

A neighbour described him as a quiet and calm man. His wife, Teresa, was said to have been excited about a coming trip to Italy to take a cooking course.

Son Rudi was an engineering student in Australia. Henri is also a student.

De Zalze Winelands Golf Estate appeared peaceful yesterday and along Goske Street, where the Van Breda family lived, children were playing.

At Terroir, a restaurant on the estate, foreign tourists paying about R200 for main courses were oblivious to the previous day's triple murder 500m away.

Dutch tourist Marcel Crince said: "A murder here? I can't believe it."

A staff member who wanted to remain anonymous said the Van Bredas were regulars at the restaurant, eating there two or three times a month.

"They were a lovely family," she said.