Storing Fruit trees

I'd be inclined to keep the roots wrapped in their packaging and just keep the roots moist until you can plant them. Check on them regularly, ideally daily to make sure they don't dry out. In the event the roots freeze don't panic just don't move them whilst frozen or the roots will snap, hopefully won't be an issue since your keeping them inside. The main thing in my opinion is making sure the roots don't dry up.

Hello and welcome.
Can you pot them up? Into buckets (with drainage) maybe? Then they would be OK until you have decided where in your new garden you want to plant them.

Guessing you do not really have much choice at the end of it all.
I would guess, and it is a guess, that you would be OK if the roots are kept a little damp, not wet, just slightly damp. Do not have them sitting in water. If the roots are wrapped with some compost around them then leave it in place.

Also would need to be kept cold.

Damp is because the fine roots will dry out and if too dry this could cause the thicker roots to perish also. So the slight damp would I hope at least maintain the roots in a undead state ready to do their job when in the ground.

I know that places sell "bare root" trees but I think these are more dormant then at present and I think the bare root trees are sort of dug up and sold ready to go in, not dug up and left around for a while.

That really is the best I can suggest and not even sure how good it is. However if it the same situation for me that is what I would attempt.

Thought just sort of appeared - might be sensible to put them in a (bigish) pot of sand in the garage, that should maintain a damp environment and also very well drained so not wet.

Not sure that saying get a decent sized pot or two and some compost would help as the pot+compost could kick them into life/growth at the wrong time of year = now.

Does your Nan have any outside space where they could be babysat for a while? Any other willing friend or relative?

I think they should be fine as it is their dormant period, are they in pots or bags? If in bags, yes you could pot them into flower buckets or similar and leave them in the garage till you move.