Hi Estee
I personally love Cederberg in the winter so in my opinion definitely doable but yes, with the right gear.
Weather can change quickly and it can get kind of cold at night (5 degrees on colder nights) potentially even snow (higher peaks more likely). But luckily on the central circuit you will have back up huts (Crystal pools, Sleeppad, Sneeuberg) in case weather turns for the worst on route. So that’s one amazing thing of having those. You also have Sanddrif, Driehoek and Algeria in the vicinity if you guys rather decide to walk out if the weather turns.
A decent 3/4 season sleep system with winter apparel would suffice 