They said the Twitter account was hacked.
"It is most unfortunate that during this sensitive time, someone would choose to hack into Oscar Pistorius's older brother Carl Pistorius's Twitter handle," said family spokesperson Janine Hills.
The tweet, which read "Thank-you to every person that has prayed for both families, Osca" and had been posted under Carl's handle, has since been removed.
"Carl did not tweet this afternoon, out of respect to Oscar and Reeva (Steenkamp)," Hill said.
Another spokesperson told Agense France-Presse (AFP) the Pistorius family is "very sensitive towards Reeva and her family and the tragic accident".
Hills said the family was cancelling its Twitter accounts. – AFP.