What is the principle for determining which grandmothers inherit when multiple are present at different degrees?
Chapter on the Roots of Inheritance Shares that Increase (Awl)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
Grandmothers inherit only when they are at an equal degree (level of proximity). If some are closer than others, inheritance goes only to the closest ones. For instance, if two grandmothers are mentioned as heirs at the closest levels, they are the maternal grandmother (mother of mother) and the paternal grandmother (mother of father).
Supporting text
If three are mentioned, they are the mother of mother of mother, mother of mother of father, and mother of father of father, meaning one from the maternal line and two from the paternal line. Only one grandmother from the maternal line can inherit, specifically the one whose entire lineage consists of mothers without any intervening father ('all her lineage are mothers with no father in them').