Is it Islamically permissible to divide the inheritance of a grandfather by allowing his grandchildren, whose father died before him, to inherit as if they were one of his own sons? Is it valid for a grandfather to grant ownership of a portion of his land to his youngest son during his lifetime? What is the ruling of Islamic law on this division, and is one who carries it out sinful?

It is permissible for a grandfather to waive his share of his son's inheritance to his grandchildren if he is legally competent to dispose of property. A grandfather's designation of certain property to some of his children is permissible if there is a legitimate religious reason, such as seeking knowledge; in such a case, those properties do not fall within the inheritance. The same applies to what he has gifted to his grandchildren, provided that the legal possession occurred before the father's death.

The grandfather's inheritance is distributed among his direct children, and the grandchildren do not inherit due to the presence of direct children. However, it is desirable to give them something from the inheritance during distribution, based on the Almighty's saying: (And when [other] relatives and orphans and the needy are present at the division [of inheritance], then give them therefrom and speak to them words of kindness). If all heirs agree to give the grandchildren a share, this is permissible as a gift and an act of benevolence, not as inheritance.

The matter of inheritances is serious and complex and must be referred to the Sharia courts for investigation, as there may be wills, debts, or rights that take precedence over the rights of the heirs. Therefore, distribution is not permissible without consulting the Sharia courts.