Watch the heating pad, don't put it right under them because it doesn't have good temp control. Put it to the side so they can hunker up next to it if they want. Of course, if it is working, you have power so you don't need it (unless you have a pretty good sized generator)
Since you have the wood stove, move the birds to an area that is close to it and high enough to get heat. I assume you have a thermometer. Put it in the box and see if you can keep them at at least 85F.
Watch them to make sure they aren't all trying to get away from the side next to the stove, that means they are too hot. If they are huddled next to the side by the stove, they are cold. If they are wandering around, they are happy. Just do like you do with their heat lamp in the brooder!
I've not had to deal with this problem, but I would also suggest a lot of shredded paper (long pieces, not crosscut) or pine shavings so they can huddle together (which they will do naturally) and the "nesting material" will help them hold heat. This isn't needed when they have a working heat lamp.
Also, you say you have a cooking stove that doesn't require electricity. I presume propane or gas. But unless it is old (like my 1932 Glenwood
) it might still require electricity to light it. "Newer" gas stoves might have a pilot that is always lit but NEW ones require electricity to spark the gas when the valve is opened so make sure you have "long lighters" on hand. Hopefully it isn't so fancy as to need electricity to allow the gas to be turned on (as a safety feature). If that is the case, it won't work at all.
You shouldn't use the cooking stove specifically to heat the house but heating water for hot water bottles would be OK. And, if you make a roast, bake some potatoes then some cookies, etc, the oven will help heat the house.
Bruce