Be careful, Martha. Social Services will want to look in detail at your Dad's assets. They will also try to look at your Mum's, though they have no right to do so. If your Mum moves into a cheaper property, they may well take half of the "profit" for care fees.
There are clear rules about this, but you may need to get some legal advice, as Social Servies have been known to make up their own rules!