What you're embarking on is not really a safari in the traditional sense, it is more a typical tourist visit to SA. You will not be encountering any of the challenges which face photogs on the Masai Mara such as dust, limited power supply, distant game, etc.
Items which I would consider to be missing from your kit are : a wide-angle lens, and a fast lens for night-time photography. The Garden Route, and Cape Town will yield some good landscape opportunities, so you really need something which will give you 17mm, or wider. Knysna, Durban, CT and the game reserve also offer a number of evening photo or historical building (interior) opportunities, so something with f1.4 or f1.8 might be worthwhile.
I also always believe it's a good idea to take along a good point 'n shoot camera.