In the context of family structure, briefly explain the various ways by which family membership is achieved.

Answers may vary. Families are defined within a sociocultural milieu that prescribes acceptable ways in which family membership is determined, roles are allocated among family members, and the functions and obligations ascribed to families are carried out.
Underlying the definition of family is a shared understanding of two elements of family structure: how family membership is composed, and the various functions that the family serves as an enduring institution in society. Following are some of the varying ways in which family membership is achieved:
Marriage, which may be an arranged marriage
Remarriage, recoupling after a separation, or blended family
Birth, adoption, foster care, or legal custody
Informal relationship, biological and nonbiological kin, friends, social networks within communities and/or cultural groups
Nannies or other surrogates in the family
Variability in families and choices can mean that households consist of single parents or two parents of opposite or same sex, any of which may be multigenerational (Carter & McGoldrick, 2005; Crosson-Tower, 2004; Fredriksen-Goldsen & Scharlach, 2001; Sue, 2006). Multigenerational families can include parents and their children and grandparents or other kin. Also, there are generational families that consist of two generations, specifically grandparents and their grandchildren (Burnette, 1999; Goyer, 2006; Jimenez, 2002). Clearly, family configurations can be as diverse as family membership.