Here are my recommendations based on several visits to SA at the same time of the year and with similar time constraints.
Land at JNB and spend the day/evening/night near the airport. Regardless of your choice of airlines or connection points, North America to JNB is a helluva long way, and jumping into a car on the "wrong" side of the road is not for jetlagged zombies.
Then choose your safari options:
1. Kruger/Sabi Sand/other northern safari destinations: Get a car and drive to Graskop, a pleasant town near the spectacular Blyde Canyon and other stops on the Panoramic Route. Stop at the Three Rondavels overlook and God's Window before spending the night at the Graskop Hotel. Note daylight hours will be fairly short as it's midwinter, so don't push the timing. The drive from JNB to Graskop takes a little over four hours on good roads; a couple of hours touring in the afternoon will give you a very full day. Why Graskop? Two reasons. First, the Panoramic Route (also called "Panorama Route") is incredibly scenic and VERY different than any other landscapes you'll see. Second, it makes for better value per travel dollar. The reason is that the game lodges provide two game drives daily, early morning and sundown. If you drive straight from JNB to any of the major reserves in the Kruger complex, you'll generally arrive too late to participate in the evening drive the first day. Thus one of the things you've paid (dearly) for is off the table. By spending the first night in Graskop, you can get to the lodge early enough the next day to have time to settle in before the evening drive. Spend two or three nights in a safari lodge, then drive back to JNB and drop the car. Here's a route map -
https://goo.gl/maps/3zQfgZ1jft72 Note I've used Elephant Plains Lodge in the Sabi Sand reserve for this map, but the results would be similar in most of the Kruger-area reserves or the national park itself.
2. Madikwe: Easier and quicker, you can make it to most of the Madikwe lodges in time for the evening drive the same day. I've shown my favorite lodge, Buffalo Ridge, on the map -
https://goo.gl/maps/L4ZQMi8mKbH2 - because it's community owned and operated, unusual among the higher-end game lodges in SA. Anyway, two or three nights there, then back to JNB as above.
I'd spend the night back at JNB before flying to
Port Elizabeth the next day, NOT Cape Town. Get a car at PLZ and drive (under an hour) to Addo Elephant National Park. Addo is a self-drive park, really quite wonderful. Spend a day at Addo, then head west along the Garden Route, a stunningly beautiful drive along the Indian Ocean toward Cape Town. Stop at Jeffreys Bay, surfing capital of South Africa (made famous in the classic "Endless Summer" movie from the 1960s) and spend the night in beautiful Plettenberg Bay.
The next day, drive along the coast then swing inland for a look at the winelands around Franschhoek and Stellenbosch; maybe spend the night in Stellenbosch, an historic university town full of interesting lodgings and great food.
Then head out to the west coast. Visit Paternoster with its picturesque whitewashed and thatched cottages and colorful fishing boats on the beach, and stop at West Coast National Park where if you're lucky the spring wildflowers will be making an early appearance. If they are, you're in for an incredible treat. Then end up in Cape Town. Keep the car long enough to visit the Capes, or see the penguins at Simon's Town. Be sure to spend some time walking around the crazy-colorful Bo-Kaap district in Cape Town and be sure to eat some Cape Malay food.
Here's a map for this final phase of the trip -
https://goo.gl/maps/8G1Cb4eNYGu
Summary of days:
Joburg - total 2 days counting overnights
Safari (Kruger area or Madikwe) - 3 or 4 nights
Addo/Garden route - 2 or 3 nights
Winelands/West Coast/Cape Town - 2 or 3 nights.
Skip Victoria Falls. It's not the best time of the year to see the falls (low flow) and the excursion is quite expensive. Use those resources (time and money) elsewhere.
Simple fact: Southern Africa is seriously addictive, so be prepared to find yourselves planning your return trip before the ink on your visa stamps is dry.