In case of son D, on his death it is his children and mother I.e. your wife B who are class- 1 legal heir of son D and property of D shall be divided among class-1 legal heir in equal proportion. However, in case of death of E I.e. wife of D, her children are only class-1 legal heir so property shall be divided among class-1 legal heir in equal proportion. If there is WILL then property shall devolve in terms of WILL.