How do the jurists of the four schools define a relative?

Kinship linguistically: It is the opposite of distance, and your kin are those who are close to you by blood relation. A man's relatives are his closest kin.

Kinship terminologically among jurists: The definitions of kinship by jurists have varied and diversified. They can be summarized into seven approaches, ranging from narrowing the scope of kinship and limiting it to the paternal side only, to broadening it to include maternal kinship and unmarriageable kin (mahram (definition)) other than parents and offspring. It may even extend to include all blood relatives, however distant, or encompass parents and direct offspring, and even marital relations, clientage (wala'), and fosterage (rada'ah).

Rights of Kinship: These are added to the rights of a Muslim upon a Muslim, and they include maintaining ties of kinship (silat al-rahim) through benevolence, visiting, kind speech, and enduring hardship.