Thank you.
No, I am not sure whether or not Alice Sarah went to South Africa. I have no confirmed sightings of her at all after 1886, and there is no marriage or death of Alice S* Wyllie in FreeBMD.
I have now, and thank you for the pointer, looked at FS for John Rupert. I had tried FS for the father and for Alice, but hadn't looked there for the son.
There are three listings, of which the third is the most detailed but for the surname being spelled Heanon instead of Heanan.
The first one, signed by the brother, gives their mother's name as Alice Sylvia Heanan, maiden name Wyllie.
It looks quite likely that my Alice Sarah Wyllie was indeed the wife of Charles Oris, or Carlos Chris, Heanan, and mother of John Rupert and C*, but I think I'd like a bit more evidence before being sure.
(The index to the third one says he died in 'Base, Solomon Islands' but the original reads 'Base Hospital Depot'

I've come across curious transcriptions before but that one is up there with the best!)