The family-chain expression “ʿan abīhi ʿan jaddihi” is common in isnāds. A narrator transmits through his father from a “grandfather,” but in some contexts the referent of the possessive pronoun in jaddihi requires independent identification.
Possibility 1: The pronoun relates to the first narrator: his father narrates from the narrator's grandfather.
Possibility 2: It relates to “his father”: the father narrates from his own grandfather, indicating a different generational connection.
Identifying the people involved requires names, dates, known teachers and pupils, and parallel chains. One should not assume a single referent for the pronoun in every family isnād.