Yes kerosene heater fumes can be bad for you if you breathe in too much of the fumes.
However a small amount of kerosene heater fumes when breathed in should do no harm to your health.
When your kerosene heater goes out or you shut it off there may be a slight kerosene fume smell that will dissipate within 30 minutes or so.
I've breathed in some kerosene fumes before and am still healthy.
Just don't breathe in too much kerosene fumes and you'll be okay.
Yes non vented kerosene heaters can be used inside a home for emergency heat.
A non vented kerosene heater will produce carbon monoxide so you should only use a non vented kerosene heater as a temporary emergency heat source in your home.
Also when using a kerosene heater that is not vented you need to allow some fresh air into the home through a slightly open window.
Just open the window a small crack to allow some fresh air in because the kerosene heater will take the good air away and replace it with carbon monoxide which is a deadly thing that you cannot smell.
They do make vented kerosene heaters too that can be used long term without the need for venting a window.
I would recommend installing a propane or natural gas vented heater that does not require electricity in the event you have a power outage and your regular furnace does not work.
As long as you use the kerosene heater safely you should be fine.