Is it permissible for my mother to take a portion of her siblings' undivided inheritance, which is in her possession, to cover the urgent medical expenses of my grandmother, and should the distribution be equal between males and females, and is it permissible for her to keep the rest of the inheritance for times of necessity, in anticipation of my grandmother's future need for money?

Firstly, the inheritance must be divided immediately, and each heir must be given their due right. This is because withholding it constitutes an encroachment upon the rights of the heirs and may lead to disputes and forbidden severance of kinship ties. It is not permissible to hoard an inheritance from distribution except for a legitimate Shar'i excuse.

Secondly, a child's failure to provide for a needy mother is an act of disobedience ( 'Uqūq). It is an obligatory act of kindness towards parents to spend on them when they are in need. If the children do not provide for their poor and needy mother, she may take from their wealth what suffices for her expenses without their permission, because "she and her wealth belong to her father" (and the mother is like the father in this regard). Therefore, if what the grandmother possesses is not enough for the operation, she may take from her children's wealth according to her need. The expenditure is obligatory upon them in proportion to their inheritance from her (the male receives twice the share of the female). If it is possible to refer the matter to the judiciary, that is preferable; otherwise, there is no sin upon the mother if she takes from the wealth of her brothers and sisters what the grandmother needs.