What is the share of each heir from the estate of a deceased woman and her son in a car accident, given the existence of a will for the mother that is subject to objection, and a disobedient brother who caused the accident, knowing that it is not known who died first?

If a mother and her son die and it is not known which of them died first, the mother's inheritance is distributed among her heirs excluding the son, and the son's inheritance is distributed among his heirs excluding the mother. This is the view of the majority of scholars. Accordingly, the inheritance of the deceased woman is divided among her mother, father, husband, and three daughters, such that the father takes one-sixth, the mother one-sixth, the husband one-fourth, and the daughters two-thirds. The son's daughter, the grandmother, and the full brother receive nothing. As for the woman's bequest of one-third of the land to her mother, it is not legally valid unless the heirs agree, based on the Prophet's (peace be upon him) saying: "There is no bequest for an heir." It is recommended to refer inheritance matters to the Sharia courts for investigation and to ensure there are no other debts or bequests.