What type of photos are you thinking for your Africa trip? Something at the safari parks? You will probably have time in Capetown or Stellenbosch for family photos. As I recall Stellenbosch has some nice architecture. We have been to SA but we haven't taken this particular trip, so I'm afraid I can't help with specific time blocks. But the vacationistas have been helpful to me in the past in letting me know when good opportunities for extra activities fall in the itinerary.
I also wanted to ask if you wouldn't mind sharing the info on the photographer you used at Angkor Wat? We have this trip on our "to do" list and I think that sounds like a great idea. On our Australia trip, I asked another guest on the trip to help with our family sunset beach photos. I am a pro photographer myself, so I set up my camera and handed it over. But it definitely would be nicer to work with someone locally.