Just a little follow up to this thread.

Availability back from CPT was very poor, often the only options I could find 355 days out was back via JNB in WTP. However last night 2 seats in F and CW for both CPT flights were released at midnight for 24 February. This morning, when I checked again, 2 F seats had already been snapped up. Called YouFirst at 7.30 on the dot, and nabbed the other 2 F seats. Really glad, but it goes to show how competitive the process is and logistically quite difficult when using a companion voucher. It really helped having flexibility and putting in the effort to keep looking. YouFirst were completely top notch, very friendly and competent.

Thanks for all the advice, and a big thank you to littlefish who was extremely helpful by PM.