Baby tortoises

[TessaRuth]

Hello and so grateful for any advice. We took on two 18 month old tortoises last January so this is our first winter with them. I know that such young tortoises shouldn't hibernate but they seem to be doing this anyway. They live in a tortoise table with heating etc, are by a window and we are in southern England. Completely on their own, they have taken themselves off and have not eaten or drunk in the past four days. Otherwise, they are perfectly healthy and have put on nearly half their weight again in the past 11 months. Should I get them up to bathe them every few days? Not at all sure what to do or whether this is just completely normal. How long is is safe to leave them like this? Really appreciate any advice. They are Hermanns.