My Uncle did not give my Dad his equal share of my grandfathers inheritance

In 2000, my Grandfather died. His will stated that my Dad and my Uncle share a house he owned equally. My uncle got the house appraised and gave my dad half the money it was worth. My Dad was recently diagnosed with Lou Gehrigs Disease and agreed without looking into it (he obviously had his mind on his illness and trusted his brother) Come to find out years later, my Uncle got the house appraised at a much lower value than the house was worth in order to have decreased property taxes. My dad received half of the money of this appraisal. Therefore, my Dad did not get his equal share. Is there anything we can do about this now?