Under the "Income" tab > "Principal Residence" then when setting up the information for the Designation you will indicate that the property qualifies for "all of the years" it was owned. There will not be a tax consequence on the tax return.

Your mother will be the only owner.

There can also be the same designation on your father's Final Return with the indication that the property was sold to a spouse. This would be for only his share of the value of the home.