Is the gift that the paternal grandmother bestowed upon the questioner's father and his uncle, to the exclusion of their sisters, Islamically valid, and how should one deal with the sisters who are demanding their share of the inheritance?

If a grandmother gifted some of her grandchildren her property and died before achieving fairness in the gift among them, the property is to be divided among all grandchildren, with the male receiving the share of two females. If the gift was not taken possession of, it becomes void, or the decision concerning it rests with the heirs. And if the grandmother bequeathed all her property to some grandchildren without transferring ownership during her lifetime, this is a bequest to an heir and is not executed unless approved by the remaining heirs; otherwise, the property is divided among all of them.