Is it permissible to distribute a portion of the inheritance during the lifetime of the inheritor to the children of deceased siblings, while reserving a portion for the brother who will inherit?

If the deceased has no heirs other than those mentioned, the brother takes the entire inheritance, for the Prophet, peace and blessings be upon him, said: "Give the prescribed shares to those who are entitled to them, and whatever remains is for the closest male." As for the niece (brother's daughter) and the sister's children, they are not among the heirs. Dividing the inheritance before death is Islamically invalid. However, the deceased could have gifted to these relatives whatever she wished from her wealth, or bequeathed to them within the limits of one-third of her wealth.