In practice the basic medieval economic and social unit was the nuclear family, Mom, Dad, Sis, and Junior as we would consider it. This was true both of peasants and lords. Others might live in their households, but this grouping was the center.
Europe and the Mediterranean, 400-800 Chris Wickham ... basic economic activity was carried out by the nuclear family;
Wickham notes that, for the early Middle Ages, it is the nuclear family that is most typically represented in our documents, with relatively much less direct reference to more distant kin.7 In Catalonia, between the ninth and eleventh centuries, the predominant type of family grouping, judging from donations to ecclesiastical foundations, was nuclear, with recorded activity of single men, men and offspring, single women, single women and offspring, and parents, either acting alone or with their children, accounting for 88.6 per cent of all such recorded activity.
Perhaps most obviously, the cadastral surveys of fifteenth-century Italy also suggest the preponderance of simple family and household structures, with 80.4 percent of households in the countryside around Florence and Arezzo composed of a single nucleus. Of families in the countryside, 51.2 percent were “entirely conjugal,” composed of parents and, potentially, their offspring.