"What happens if you are living in that house, caring for your parent? "
Eh? So dad dies and mom is still in the house? Doesn't apply. The tax doesn't kick in until she dies.
"Currrently, the tax applies only to taxable estates over $1.5 million, that is, estates over $1.5 million after debts, final expenses, charitable bequests and bequests to a spouse have been subtracted. Because an unlimited amount may be transferred tax free to a spouse, the tax is typically paid only once a generation, when the second spouse dies."