How are shares distributed when the heirs include those with fixed portions and uncertainty exists regarding other heirs or the extent of fixed portions?

Primary text

When uncertainty exists, the certain portion is granted. If a wife exists, she receives one-eighth of the one-fourth share (i.e., one-thirty-second), as it is possible he had four wives. If a grandmother exists but the death of the mother is not proven, she receives nothing. If the mother's death is proven, the grandmother receives one-sixth divided by three (i.e., one-eighteenth), as it is possible there are three grandmothers. Heirs receiving residual shares (*'aṣaba*) receive nothing because of the possibility of an heir existing who would exclude them. If the heir is a brother, he receives nothing due to the possibility of an heir who would veil him (exclude him). If a mother is present, she receives one-sixth, subject to potential reduction in the case of mutual claims (*'ā'il*), and the wife receives one-eighth, also subject to reduction, as this represents the certain portion. The husband receives one-fourth, subject to reduction, because this is the certain amount. This is because the case can become one of mutual reduction even with the husband present, such as if there are two parents, two sons, and a husband.