We use an electric blanket on our bed in cold weather. What you think is cold is probably not what we think of as cold but we have camped at temperatures below 20 degrees often. Besides the electric blanket we have a comfortor that goes on top of it if needed.
We have a small space heater that we take with us to supplement our furnace in case we run out of gas.
If it is really going to be cold take gloves or mittens for everyone when they go outside.
Take warm pajamas. If you do not have warm pajamas, use sweat suits as pajamas.