Central to the concept of family coexistence is the development of its young members' selves through a process that occurs in the family's shared life and activities. In this process, young persons are socialised into their family's values, capabilities and expectations at the same time that they experience their family's care and support. What possibly emerges from family coexistence is youth's personal agency that is exercised for prosocial goals. This hypothesis is examined in this paper in the Philippine culture, where other persons are regarded as shared selves and the family's function of educating children is considered of prime importance. Self-report survey data generated through the Multicontext Assessment Battery of Youth Development and from three separate Filipino undergraduate samples show support for three models (a) a correlated two-factor model of family relations and capabilities, (b) a correlated two-factor model of youth's agency and prosociality, and (c) a structural equation model suggesting a developmental pathway starting from positive relations onto socialisation in family capabilities; family capabilities then directly influence youth's agency that, in turn, directly influences prosociality. Thus, while youth's prosocial self emerges from the interpersonal and communal nature of family coexistence, it also is shaped by youth's exercise of personal agency. The results are examined in the light of agency and prosociality as bases of the integrality of the self.
