Am I entitled to revoke my mother's waiver of her share of her son's inheritance to his children, given that there is a medical report and witness testimonies proving her lack of legal capacity to act at the time of the waiver, especially since the witnesses to the waiver are not related to her by kinship, neighborliness, or dealings?

The mother's actions before she was legally declared incompetent by the judge are considered valid and are presumed to be guided by rationality and benefit; you do not have the right to revoke them. This is because the actions of a legally competent person are presumed to be guided by rationality and benefit unless there is evidence to the contrary or a judge rules them incompetent. Furthermore, it is not a condition for witnesses to be relatives or neighbors; rather, the conditions for them are justice, absence of immorality, and freedom from anything that compromises integrity.