The said will of your grandfather is null and void, as will cannot be made in favour of heirs. All the four sons and three daughters will inherit the property of your grandfather.
In case the question is related to only second deceased son and his inheritance, then his all the property shall be divided into 8 shares. Out of which 2 shares shall go to his wife and 2-2 shares to his each brother and 1-1 share to each sister, provided none among the parents of the deceased was alive at the time of his death. And then the inheritance of deceased wife shall be divided among her Shariah heirs. The detail of second brother’s division is as follows:
Wife: 1×2 = 2
Brothers: 2×2 = 4
Sister: 2×1 = 2
Total: 8 shares
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband