Short answers, pulled from the story.
In anthropology, kinship is the web of social relationships that form an important part of the lives of all humans in all societies. It can refer both to the patterns of social relationships themselves and to the academic study of those patterns. Kinship includes relationships formed through descent, marriage, and, in many cultures, co-residence and nurture.
Lewis Henry Morgan identified six major kinship terminology systems in his 1871 work Systems of Consanguinity and Affinity of the Human Family: Iroquois, Crow, Omaha, Inuit, Hawaiian, and Sudanese. A seventh system, Dravidian kinship, was identified as distinct later. These systems differ in how they categorize and group relatives under shared or separate terms.
Descriptive terminology uses a term to refer to only one specific type of relationship; for example, 'brother' in English refers only to a son of one's same parents. Classificatory terminology groups many different types of relationships under one term; in many systems, a male first cousin through any parental line may also be called 'brother'. Morgan identified this distinction as one of the most lasting contributions to kinship studies.
Anthropologists recognize four main descent rules: bilateral (tracing through both parents equally), unilineal (tracing through one sex only, either patrilineal or matrilineal), ambilineal (allowing individuals to choose which line they affiliate with), and double descent (recognizing both patrilineal and matrilineal groups simultaneously for different purposes). The Afikpo of Imo state in Nigeria are a widely known example of double descent.
In his 1984 book A Critique of the Study of Kinship, David Schneider argued that anthropology had embedded an ethnocentric assumption into kinship studies since Morgan's earliest work: that 'blood is thicker than water' is a natural and universal human value rather than a culturally specific one. Schneider contended that Western anthropologists mistook their own cultural values about biological relatedness for universal facts, potentially undermining the entire enterprise of kinship as a cross-cultural category.
Nurture kinship is the concept that kinship relationships can be created and maintained through acts of care, feeding, and living together, rather than solely through biological or genealogical ties. The Malays of Langkawi, studied by Janet Carsten, derive relatedness both from procreation and from living and eating together. The Temanambondro of Madagascar, studied by Philip Thomas, similarly treat nurturing processes as a basis for kinship ties. The Trobriand Islanders, as recorded by Malinowski, recognized fatherhood as a social and nurturing role even without acknowledged physiological paternity.