An alleged gang leader and his 11-year-old son were gunned down in Lavender Hill, sparking fears in the community of a possible retaliation.
A third victim in the shooting that took place on Friday sustained injuries and was taken to hospital, according to the police.
Police spokesperson Captain FC van Wyk said the motive could be gang-related.
A community member alleged that the murdered man was the leader of Fast Guns, one of four gangs including Mongrels, Junky Funky and Plaka that operate in the Lavender Hill area.
Community leader Howard Soetwater said he was told by the family of the deceased that a man known to them entered the house on Friday afternoon and opened fire, killing the 42-year-old man, his son and injuring another minor, aged about 6.
"It was apparently gang-related and the alleged perpetrator was released from prison a few weeks ago," claimed Soetwater.
He described the situation in the community as tense and said police were deployed in the area to restore calm.
"The community is angry at the killing of minors. We are now worried that the members of the Fast Guns gang will retaliate and innocent people will lose their lives," said Soetwater.
Chairperson of the Community Policing Forum Gavin Walbrugh called on the community to remain calm.
Walbrugh said although more law enforcement agencies were expected to be deployed later in the area, community members were "edgy" as they expected retaliation at any time.
"These retaliation attacks happen after a burial, but the area remains tense."
He also called on those with information that could lead to the arrest of the perpetrator to assist the police.
The community has in the past made several calls on the provincial government and SAPS to ensure safety in the area.
In July the residents of Lavender Hill marched on the Steenberg police station demanding better policing in the area and a change in management at the police stations serving their community – Steenberg and Muizenberg police stations.