بسم الله الرحمن الرحيم
If the parents of your wife have passed away, then the will of her father shall be accomplished from 1/3 (one third) of whatsoever property and land etc he left behind i.e. one third of his property and wealth shall be spent in any good deed for the isal-e-sawab of your wife’s parents such as for the construction of mosque, madrasa etc, while the remaining two third shall be divided into three shares; out of which 2 shares shall go to the son and one share will go to the daughter. However for easy division you may also divide all the property into nine shares. Out of the total three shares shall be reserved for good deeds. While the son shall get 4 shares and the daughter 2 shares.
Since the will of one third for the son and one third for the daughter made by the father is in favour of heirs hence it shall only be enforced when the second heir (son) allows it happily. If he permits it happily then there is no need to divide it into nine shares as per the aforesaid method; rather then it shall be divided into three shares and distributed as per the will.
Allah knows Best!
Darul Uloom Deoband