Before you do anything, invest in a CO2 monitor. If you plan to use propane, kerosene or butane indoors, invest in an explosive gas detector with a CO monitor.

If you already have a propane tank from a BBQ then a tank top heater is the cheapest and easiest route to go. They are very small to store, most are smaller than a basketball.

A full 20lb tank can heat a fairly large room, 150 sq feet. It will last anywhere from 32 hours at full blast to a week being rationed as the room gets warm.

The same tank can be used with a camp stove to prepare food. They even have dual purpose heater/stove units for emergencies

That being said, you can move everyone into a single room, cover the windows in bubble wrap and heavy curtains or blankets and create a single room where body heat is conserved. Even cardboard and bath towels will help as insulation on thin windows and walls. Having rugs or comforters in the floor helps with keeping warm also.

Each person should have either a three season sleeping bag and a fleece sleeping bag liner or a wool blanket bedroll. Each person should have a pad of Reflexix to sit or lay upon or some other way to insulate themselves from the ground. This is assuming there isn't enough sleeping space for everyone that is elevated.

Sleeping in tents, blanket forts and such lower the ceiling and make a smaller space to heat. Smaller spaces make it easier to maintain an even temperature with just body heat. NEVER put a heat source inside a tent or blanket fort. Heat sources should be kept at least 24 inches away from tents and blankets.

Each person should have a set of heavy winter clothing. Heavy socks or wool socks. At minimum, a decent head covering you can sleep in will help maintain warmth as well as having a pair of mittens you can sleep with.

Each person should have a set of warm underwear, long johns or at minimum a set of sweats to sleep in. Ideally, when camping, I have a set of large sweats I pull on over my clothing, so I'm never stripping down. Looks don't matter when you might freeze.

Having a dual burner propane camp stove or a small single burner butane stove will allow you to cook. There are other ways to cook off grid but both of these are easy to use and familiar enough there isn't a learning curve. Fixing food and eating will warm to body and raise moral. You won't want to skimp on food. Be sure you have enough to drink AND be sure to have enough water to use in cooking as well.

If you have kids especially, have entertainment that isn't dependent on power. Coloring books, ebook readers, knitting/crochet, puzzles, cards and an emergency radio can go a long way to keeping kids occupied.

Have plenty of extra batteries if needed and think about investing in a folding solar panel and battery bank. Save your phone for phone things and emergencies, not useless games that drain the batteries.

And most people think about staying warm during power outage in the winter. Everyone forgets about sanitation. Baby wipes are a short term solution for power outage but it won't help if the water stops running, you will still need a toilet. A 5 gallon bucket works great when paired with a urinal for the guys. Don't use kitty litter. It is heavy and doesn't help the smell. Use compressed pine pellets or light pine shavings. Pine absorbs well and doesn't promote smells. They sell actual toilet seats for buckets but you can check online on how to DIY one.

And something VERY important. Do not wait until the power goes out to test all of your stuff. Make sure you know how to set up the toilet, how to turn on and off the heater, what food is good to cook on a camp stove. Have the kids practice setting up a blanket fort so they know what to do ahead of an emergency and it isn't stress it is fun!

But didn't forget the CO monitor or the combo explosive gas detector/CO monitor