Since they are buried in Durban, I assume they lived there. There is no online census data in South Africa to my knowledge.
However, if you do a search online including their names and perhaps Durban or Natal, you are quite likely to find something like marriage information etc.
Also SA National Archives NAAIRS. Search under Winton. I noticed that some spelling seems to be Cullan. These documents would need a researcher to obtain a copy if you require. I love too far from Durban to help !