Don’t need them to burn for very long, cotton should have roughly the same energy density as wood by weight. Burning bags of cold clothes that don’t fit isn’t that bad of an idea.
Negative teens is brutal, even a well insulated house loses a lot of heat if you want it comfortable but there’s a big range between uncomfortable and dead. -15f to 30f is the same difference as 30f and 75f.
which means they'll provide a few minutes of heat at best. You'd be better off using them as blankets or letting some water freeze them into scoop shapes and turning them into makeshift shovels.
They also aren't going to burn nearly as cleanly as wood, meaning the burn will be far less efficient.
Depending on the size of area that you're heating, getting from -15 to 30F will take at least a solid hour of burning cleanly.
It isn’t going to be clean burning, but the clothes are presumably bone dry which helps.
Really though it’s not about how good an energy source this is, but just how much old junk people have. I have seen people toss several hundred pounds of old clothes that don’t have any real value. It’s the same with old books they don’t burn that well but when you have a half a ton you might as well burn em vs toss them in a landfill.
If they had several hundred pounds of old clothes they can build a gigantic pillow fort and huddle together in the middle with a candle.
This would be better than burning the clothes, as I assume they have enough food.
Insulation doesn't provide warmth, it only reduces the rate of heat loss. If it's already so cold you are looking for things in your home to burn for heat, using clothes to insulate it (rather than burn them) isn't going to help.
But that's not the point, the dire situation with little support is the point.
You don't insulate the house; you insulate your body. If you're at the point of burning clothes to heat the house, heating the house is already a lost cause unless you have a lot of clothes.
