Where does the money come from to pay for the nursing home care?

I am ahead of myself in this thinking but I have a feeling at some point soon my father is or will need to be put in a nursing home (maybe within a year or two depending on how much more my mother can handle). I am sure I will need to check with an elder attorney BUT if my father would go into a home and my mother is still living, where does the money come from to pay for the nursing home care? I would hope my mother would not be kicked to the curb from her own home. And what happens IF mother would pass away and father in home, do we sell the house and if so/who gets all the money, just use what we get to pay for nursing care and when its all, its all? just trying to get a hold on how to handle some things. thanks