If a man marries his maternal aunt’s daughter and she bears him a child, that child’s grandmother is both the mother of the mother of the mother of their child and the mother of the mother of his father. If he marries his paternal aunt’s daughter, that child’s grandmother is both the mother of the mother of his mother and the mother of the father of his father.

His statement, “If a man marries his maternal aunt’s daughter and she bears him a child, that child’s grandmother is the mother of the mother of the mother of their child,” means: the child of both the wife and the husband.

His statement, “and the mother of the mother of his father”: an example is a man who marries his maternal aunt’s daughter and has a child by her. The child now has two grandmothers: a grandmother on his father’s side and a grandmother on his mother’s side. The grandmother on his mother’s side is, for the child, the mother of his mother’s mother, and she is also the mother of his father’s mother. She therefore inherits two-thirds of the one-sixth, while the other grandmother, who is related through the father’s side only, inherits one-third of the one-sixth.

His statement, “If he marries his paternal aunt’s daughter, that child’s grandmother is the mother of the mother of his mother and the mother of the father of his father”: this is clear.