A mixed family is formed by the merger by official or de facto marriage of two or more family remnants from previous marriages or family constellations. At least one of the spouses has had a parental role in a previous family system and brings into the blended family a child or children from that union. Mixed families vary considerably in their composition. The children may belong to the wife or husband by prior family union or may be theirs by present arrangement. Since custody is normally awarded to the mother, the typical mixed unit consists of a wife, her children, and the husband, whose children, if any, reside with her mother.

With the growing popularity of joint custody and the increase in the number of serial family relationships, blended family configurations are becoming more varied and complex. Many children now belong to two households, splitting their time evenly between the two. In some families the children of two or more previous marriages retain their paternal surnames. Therefore, numerous surnames can be used within the same family, which significantly affects the bonding and identity formation process.

Blended families can be extended families with exponentially complicated structures, although the term is normally used primarily to refer to newly formed nuclear families that are made up of integrated subsystems of earlier family units. The main challenge of the blended family is to become a cohesive unit. However, it must be defined by boundaries that allow appropriate contact with what is often a large and disjointed network of relatives in the new extended family. These families must negotiate several critical developmental tasks to come together.

One task facing all members is mourning the lost families they represent. Family failures and breakups are severe emotional traumas, and this loss requires substantial grief if one is to be prepared to invest in new relationships. Blended families often arise from relationships motivated by the rebound of forming relationships in an effort to escape the pain of loss, loneliness, and the shame of failure. Although one may have cognitively accepted the termination of a previous family union by death or divorce, the new relationship symbolizes the old loss and failure. Out of loyalty to the new relationship, one can repress that grievance/loss, but that simply constipates and subverts the residual grievance. It will surface in some destructive way at a later time.

This grieving experience can be particularly true for children, who often grieve a lot after a family breakup. This is seen in the persistent longing to be reunited with the absent father and in the ongoing fantasy that the child’s mother and father will eventually remarry. It is also manifested in the refusal of some children to form a relationship in the new family constellation or with the stepfather. The inconclusive grievance tends to bias the child’s loyalty exclusively toward the natural parent. This usually produces destructive counterforces in the entire family constellation. Unresolved grievance is poison to the blended family. It produces intra-family tension and diverts emotional energy that could otherwise be channeled to strengthen family relationships. Professional help is often needed to resolve this type of grief due to its insidious nature.

A fundamental developmental task for spouses is to form a strong marriage bond. Continued contact with the ex-spouse and ex-in-laws, for example, in the course of normal child visits, can be detrimental to the development of the new marital relationship. Jealousy, trust, and loyalty issues are easily triggered by these continual contacts. However, the cornerstone of the blended family is the quality of the new marital union. Furthermore, one dimension of this conjugal union is the development of a co-parenting partnership for the care of each other’s children that is strong enough to withstand repeated counterforce dynamics injected by the children, who probably still have their own pathological and unresolved agenda to act or resolve. Children more readily accept a stepfather if their natural father demonstrates an unwavering commitment to the marital relationship and its long-term viability. Children often create conflict between the father and the stepfather, maneuvering to gain the support of the natural father. Feelings of loyalty and guilt on the part of the parents, particularly for having failed the child by failing in the previous relationship, tempt the father to side with the child against the new spouse. This type of triangulation is always destructive.

Maintaining a “mine/yours” view of children undermines the stepparent-stepchild relationship. It places the stepparent in the untenable position of having to borrow the authority of the natural parent when it comes to stepchildren. This obstructs the process of true fusion between the new spouses, as well as between all the members of the new family constellation. Triangulation produces division.

Furthermore, building functional step-sibling relationships is complicated by the fact that the ordinal position between siblings and the entire genogram structure for the new family will change vastly with the amalgamation of family remnants into the combined family. Sibling rivalry may subside as the rest of the family closes ranks for this new experience, but step-sibling rivalry often escalates, painfully changing the roles, identities, and self-perceptions of all children. A related problem for blended families with adolescent or young adult children living at home as part of the family constellation is the fact that children who might be dating live together as siblings. Sexual boundaries are often weak, as blended families may not have well-established inherent incest taboos. Conflict and rivalry are ways teen step-siblings define boundaries to protect themselves from anxiety and the threat of excessive intimacy. Many blended families achieve harmonious, well-adjusted relationships, although the usual critical adjustment time period is two to four years.