What is the precedence between sisters and the father for custody?
Chapter on Who is More Entitled to Child Custody
Al-Mughni
Book of Maintenance (Nafaqāt)
Primary text
The full sister or the sister through the father is preferred over the father. The established view in the school is that sisters take precedence over brothers in the same degree of relationship because the sister is a female relative eligible for custody, similar to how the mother is preferred over the father, and the father's mother over the father's father.
Supporting text
There is an opposing view suggesting that the sister should be secondary to the father because the father is an inheritor through the male line (Asabah bi-nafsihi), but the first opinion, giving preference to the sister, is superior.