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This paper explores the shift in family influence on socio-economic outcomes, focusing on sibling relationships, from the sixteenth to the nineteenth centuries in the Barcelona area. Our findings reveal a diminishing role of vertical ties (parents–children) and an increasing significance of horizontal ties (between siblings). Specifically, brothers who were first in the sibling group to marry exerted more influence on socio-economic persistence over time, aligning with the changes in familial dynamics since proto-industrialization. Gender dynamics highlight the influence of first-married brothers’ influence, although first-married sisters were also significantly associated with non-first-married siblings’ social mobility. The intensification of horizontal ties is seen as a cooperative model among siblings, challenging the notion of a complete loss of family influence during industrialization. The study contributes nuance to modernization theory by highlighting the enduring importance of kinship in industrial periods, especially among siblings.