Moving rabbits from indoors to outdoors in Jan

Hello all, my mum and I recently moved into rented accommodation. We still have a house (long story) where the rabbits are still living but as we are not staying here, and have moved all our belongings to the rented place, I have been thinking of what to do with Gwen and Finn. We don't know if we will be staying in rented (again, long story) so I have been stuck coming and going between the two places multiple times a day. The landlord says no pets, but I am willing to try and sneak them in for the winter. Although I do get a little nervous with the thought of the landlord turning up and them potentially chewing up the carpets etc. Things are also a bit of a mess there, with moving boxes and such still piled around. I don't like the idea of moving them into a hutch in the garden at this time of year, especially with all the horrible weather we've been having lately. However, there is a little garage at the end of the drive at the rented place that could be an option. Obviously, it still isn't as warm as a house but it's solid and dry and even has a large window to allow light in. If I were to get a hutch with a microwave cozy for them do you think that would work? Or should I A) continue keeping them at our old house or B) sneak them into the flat for a few months until the weather warms up. Gwen is still under a year old and I don't believe she has developed any kind of thicker winter coat like Finn has since he's a little older so I am very worried about her being shocked by the temp change.

I think it'd be too big of a difference this time of year, since the garage would still get quite cold, especially at night, and a microwave cozy only stays warm for a couple of hours in my experience. Maybe if you gave them lots and lots of straw to keep them warm? I'm not sure... Maybe someone with more experience with outside rabbits can tell you if it's okay. On the other hand, it sounds risky to sneak Gwen and Finn into the flat when the landlord says you're not allowed to have any pets, but I understand that going back and forth between your current house and your old house multiple times a day is not ideal, either. I hope someone else has a more helpful answer for you.

I'm thinking out loud, but what if you could set up a tent in the garage, maybe cover it with survival sheets or other lightweight reflective insulation, and then have a small oil-filled radiatior in the tent? Effectively making them their own heated "room" to transition in. Fence a pen inside it, floor it with thick straw perhaps, and give them plenty of boxes of hay and straw to snuggle into - box within a box with straw between the layers for insulation too. I don't know if over time you could very gradually drop the temperature as they acclimatise, but at least you'd only be heating that area and not the whole garage - or presumably the whole house if they are still living elsewhere? You could drop the temperature slowly at the house they are in before they move too?
I don't know that they would grow a suitable coat now, but there is a vast difference between being in a garage and actually being outside, so I'd have thought that done slowly you could transition them to have the garage at least, with some heating.