The attack was assumed to have happened between Wednesday evening and the early hours of Thursday morning.
All four of them were allegedly beaten to death. They had sustained blunt force trauma, said Captain Appel Ernst.
“The 73-year-old male was allegedly visiting South Africa after his family emigrated to the United Kingdom a few years back,” Ernst said in a statement.
The man’s family in the UK became concerned after he failed to return their calls. A family friend was asked to go and check on him at the farm.
The friend discovered the elderly man’s body on the property and alerted the police.
“During investigation on the scene, the [son’s] fiancé was found in a partially built house on the premises,” said Ernst.
The 46-year-old woman was dead.
Police officers continued their search around the property and little girl was also found.
“The body of the child was discovered in a shed,” Ernst said.
A search was conducted for the elderly man’s son for hours on end but there was no sign of him or the family’s Mercedes SUV.
The abandoned vehicle was later traced to the Greenhills area, more than 40km away from Doornfontein.
The police’s K9 unit as well as a helicopter were deployed to the area to search for the missing 42-year-old man.
The man was still nowhere to be found on Thursday.
On Friday, police conducted an aerial search for the man over the farm. His body was eventually located in a grove on the property.
At this time, his family from the UK had already arrived on the scene.
Nothing else but the family’s vehicle, which was later found abandoned, had been taken from the property, Ernst said.
No arrests had been made.