Rapid urbanization in the Global South has fundamentally transformed family structures, intergenerational relations, and value systems. While governments increasingly introduce policy frameworks to promote family well-being, such initiatives remain predominantly technocratic, prioritizing measurable socioeconomic indicators while overlooking the cultural and ethical dimensions that sustain relational life. This article develops a theoretical framework of cultural governance of family well-being, arguing that sustainable family policy in megacities must integrate institutional design, community mediation, and familial value formation. Drawing on Aristotelian virtue ethics, interpretive cultural theory, and family resilience scholarship, the study reconceptualizes family well-being as a culturally embedded process of human flourishing rather than a purely administrative outcome. Using the context of rapidly urbanizing Asian megacities as an analytical reference point, the article identifies key urban value tensions—including economic instrumentalization, intergenerational divergence, demographic aging, and digital individualization—that challenge normative continuity. In response, it proposes a Family–Community–State triadic governance model grounded in ethical alignment and participatory legitimacy. The article contributes to urban governance and family policy scholarship by offering a culturally grounded framework applicable to developing megacities seeking socially sustainable futures.