Are the heirs of the paternal uncle obligated to carry out his oral will to his sisters to give them a share of land that they had previously officially relinquished to him?

If the adult, competent sister relinquishes her share of the inheritance to her brother, and the brother takes possession of this share, then the gift is complete, and her children have no right to claim it. As for the brother's statement that he would give his sisters their share, if he intended to do so during his lifetime, and he died without giving them anything, then they have no right to it because the gift was not completed. If he intended to do so after his death, then this is a will that is only valid up to one-third of the estate if the sisters are not heirs. In case of dispute, the matter must be referred to the Sharia court or to a qualified scholar capable of adjudicating.