Kerosene heaters are safe to use indoors for short term emergency heating situations such as when the power is out.
But Kerosene heaters should not be used as a sole source of heat unless the kerosene heater you're using is a direct vent, vented kerosene heater that vents to the outdoors.
Using an non vented kerosene heater indoors is okay for emergency use but you should crack a window to allow some fresh air inside the house while it's operating and keep anything flammable away from it and shut it off before going to bed.
A better option though for emergency heat is to have a natural gas vented heater or propane vented heater that uses no electricity to operate or even a wood burning stove.
You could also have an emergency backup generator installed to your home that will come on in the event of a power outage to keep your furnace operating as well as other electricity in the house.