I'm on the 500GB + 500GB @ R500 p/m. According to the app this plan is called: My MTNchoice 400GB.
It seems like only 100Gb is shareable since I have the following bundles (excluding night data):
My MTN Choice Anytime 5G (Expires 31/01/2021) - 226.67GB
Promotional Data - I used up this data...