Sun and warmth will wake them up, then they will take up water again. Make sure they haven't lost their roots, that soil looks very peaty. Small clay pots dry out very fast and peat may be difficult to re-wet after it becomes very dry, give them a good soak once the weather is safely warm.

Gymnocalcium will visibly shrink during the winter--they survive off the water they have stored inside and are dormant. Until you see flowers or other signs of growth don't water again. They will let you know when they are ready to come out of hibernation. If you're worried, start off by spraying them with a spray bottle a little. Don't water a ton right away, b/c roots dessicate a little during the winter, give little sips at first to ease it back into the growing season--otherwise it could rot.

Hope this helps!

Here is a link that might be useful: short gymnocalycium info

Yes thanks for your help!