Overwintering my trees.

I have some trees. Some says to be Zelkova. I have 3 of them. It has the typical s shape. I keep buying them, cause they are cheap. Here in Norway, I cant really find much to buy, and it gets way to expensive to me. So I buy some of those cheap ones, and see what I can do. And I get some yamadori.
I have a blackthorn, which I planned to let be outside over winter. Same with my oaks, and needle trees.
I have a few figs that will be in my windowsill. Mostly bedroom. Its cool, but I guess its better than the dry air in the livingroom from the fireplace.
My fukien tea will change places now and then, between the last two.
But the zelkovas, my small sageretia, and azalea? Zelkovas are inside, the others are outside. This morning I had a temperature when I left for work, at about minus 8.5 c. Also, Ive had about 5 cm of snowfall during the last hours. Stopped now.
Any tips on how to do this will be nice. I dont have a usable greenhouse, a garage or anything. Its either outside, or inside.
Id hate to keep losing trees every winter. Last year, I lost several, cause of the dry air inside..

As I recall, you have a rather mild climate. The zelkovas should be outdoors with some protection. Azaleas depend on the species. They might do best in a cool greenhouse. Do some research on Sageretia. The figs will definitely prefer a cool windowsill. The Fukien tea may be a problem. Does your greenhouse have a warm section?
Iris