Will the grandfather be punished for registering all his property in his wife's name, thereby depriving his children and grandchildren of their rightful inheritance, and will the grandmother be sinful if she does not give her children their share of the inheritance?

If the grandfather endowed his property to his wife while he was in full legal capacity and she took possession of the money, then the endowment (hiba) is legally binding, even if it constitutes all of his wealth, and the consent of the heirs is not required. However, if his intention was to disinherit the heirs, this is not permissible in Islamic law, but the endowment remains valid, though there is a difference of opinion among scholars on this matter. If the wife knew of his intention to disinherit the heirs and accepted the endowment, then she is sinful for assisting in a transgression. If the written document was a will taking effect after death, then it is a bequest to an heir, which is not valid unless approved by the mature, sane heirs.