Thanks for the suggestions. I've tried to convince my parents of this, but they will not budge. When they will start this, they will also be leaving JNB for good so will be very busy sorting out moving, taking care of our animals, sorting things out, transporting cars, tying up lose ends and so on. Despite having done this sort of thing many times, it still stresses them out immensely, and the last thing they want to do is go to Zimbabwe (especially with all the crap their beloved leader is currently orchestrating). They will eventually be ending back up in/around CPT to settle down. This also makes date flexibility difficult because once the house is empty, they have little desire to live in a hotel.

Regardless, one D seat has become available on the date they need/want to fly, so the agents have recommended splitting the ticket into two PNRs so one flies in D on the day, and another possible leaving a day or so earlier or later in D as well, or suffering in economy (probably my mother, who is more used to economy while my dad has not set off behind the curtain as long as I can remember ).