Biographical inquiry extends beyond fathers and sons. Brothers and sisters may appear in related chains and may be identified through different family names.
Al-ikhwa wa-l-akhawāt is the study of sibling relationships among transmitters.
A dedicated work on the subject is attributed to ʿAlī ibn al-Madīnī. Such research clarifies whether two transmitters were siblings, shared a parent, or belonged to the same household.
Family relationship does not automatically prove that one heard a report from the other. As with tribal affiliation, it is useful evidence of identity rather than a substitute for establishing actual transmission.