You can deduct mortgage interest and real estate taxes as an itemized deduction regardless of whether there is a nanny living in your home.
If the nanny is required to pay fair market value rent for the room she lives in, you could deduct a proportionate amount of your household expenses as a rental expense (by the percentage of the home she occupies). The mortgage interest and real estate taxes deducted as an itemized deduction would need to be reduced by whatever amount is deducted as a rental expense.
Otherwise, household expenses besides mortgage interest and real estate taxes are not deductible.
