i dont think these would last even autumn here Joburg gets pretty cold here,i wouldnt even trust leaving them to close to a window indoors.
I bring my Cym in when there is a threat of frost. Mine both bloomed reliably every winter. But I only have one now. It gave me two spikes this year. I wouldn't stress yours too much, especially if they are struggling.
Is it possible to move your Cyms in an area with a protective overhang or against your house? Our area has mild winters too, but we are inland as well. Typically we get a few hours of winter temps at 39F (3.8C) or there were times we did dip into 21F to (-6C). Then come winter to spring transition, the temps swing hi-lo wide and sometimes some hail event.
My mini-cyms endure, and I also see another neighbor with cyms always with profuse blooms this time of the year to Spring. Her cyms are against their house.
When I attended a Cymbidium repotting lecture one time, the speaker said, not to worry much about Cyms since they are really tough, and native to the foothills of the Himalayas and some mountain areas of South Asia. I always keep that in mind now, so I do not panic much when temps go low in winter.
looks like over zealous waterers are their biggest threat lol but i shall overcome.on the upside one of my cattleyas(Alma Kee) is in bud so ive got some good news.
Due to lack of indoor space, I keep my Cattleyas in my green house all year. I keep it above freezing but it is often in the low 30 - 40's at night.
They have grown and bloomed throughout the winter.
I know this isn't ideal but the ones I have seem to be quite adaptable.