Lilach Shwartz-Peleg, Varna Free University, Bulgaria
published in the Proceedings of the 3rd International Conference on Love and Relationship Studies, 6-8 March, 2026
You can see the full video recording of this presentation at the YouTube channel of the International Institute of Love Studies
Introduction
The study explores the emotional and systemic changes in family love when new members, such as in-laws, join the family system. Drawing on family systems theory, and particularly on Bowen’s concept of emotional differentiation (Bowen, 1978), this study examines how adult siblings renegotiate boundaries, loyalties, and emotional closeness following the entry of in-laws into the family system. Emotional differentiation is conceptualized here as a key regulatory capacity that shapes siblings’ ability to remain emotionally connected while navigating shifting alliances and relational expectations during family expansion.
The aim of this study is to examine how the entry of in-laws reshapes adult sibling relationships, by examining key relational mechanisms that become activated during family expansion. Specifically, the study investigates how emotional differentiation, parental attitudes, and siblings’ conflict resolution skills function as key relational processes through which in-law integration influences sibling closeness, communication, and relational stability.
In this study, in-law integration is conceptualized not merely as the addition of new family members, but as a systemic transition that alters existing family boundaries, loyalty structures, and relational expectations. By focusing on these psychological and relational processes, the research seeks to clarify the conditions under which love, belonging, and relational equilibrium among adult siblings are preserved, challenged, or fundamentally reorganized within expanded family systems.
Methodology and Methods
The study employed a mixed-methods design that integrated quantitative and qualitative approaches. The quantitative phase included structured surveys completed by 114 adults, all of whom had at least one married sibling. In this quantitative phase, participants completed a structured questionnaire battery composed of standardized instruments (Differentiation of Self Inventory; Knauth & Skowron, 2004; Sibling Relationship Questionnaire; Furman & Buhrmester, 1985; Conflict Intelligence Self-Assessment; Velasco et al., 2019; and a Parental Favoritism Questionnaire adapted from Bedford, 1992, and Deering, 1991).
For example, the survey included the Differentiation of Self Inventory (to assess emotional differentiation), a conflict resolution skills scale, and a sibling relationship quality questionnaire evaluating aspects like communication and emotional closeness. Participants responded using Likert-type response formats (4- or 5-point, depending on the measure), producing numeric scores for emotional differentiation, conflict resolution ability, sibling relationship quality (including communication and emotional closeness), and perceived parental favoritism. This survey assessed patterns of emotional differentiation. The measures assessed emotional differentiation, conflict resolution skills, and perceived quality of sibling relationships, including communication patterns and emotional closeness.
The qualitative phase consisted of 15 one-on-one, semi-structured in-depth interviews (approximately 45–60 minutes each) exploring participants’ lived experiences of family reorganization. An interview guide organized questions around the aforementioned themes (boundary changes, loyalty tensions, shifts in roles, etc.), while still allowing participants to narrate their personal experiences freely. For example, some interviewees described feeling a loss of closeness or temporary jealousy when an in-law entered the family, whereas others shared stories of improved communication and newfound family cohesion over time. These open-ended responses provided rich, narrative context illustrating how siblings experience and adapt to the integration of in-laws. The interviews were analyzed using a thematic analysis approach, enabling the identification of recurring patterns and central themes across participants’ narratives.
Highlights of Results
The findings of the study reveal that the entry of in-laws into the family system often reactivates early sibling roles and attachment patterns. Quantitative analyses revealed significant associations between higher levels of emotional differentiation and more adaptive sibling communication, greater emotional closeness, and more constructive conflict resolution.
Qualitative findings further illustrate how siblings navigate tensions related to loyalty, perceived exclusion, and boundary ambiguity, alongside opportunities for relational growth and redefinition of sibling bonds.
The results showed that families characterized by higher emotional differentiation demonstrated greater adaptability, empathy, and cooperation, while families with unresolved sibling hierarchies or parental favoritism experienced increased tension, exclusion, or rivalry. Quantitative analyses confirmed significant correlations between differentiation levels and the quality of sibling communication, whereas qualitative insights illuminated how love, loyalty, and belonging are renegotiated in adulthood. Together, these results highlight the delicate balance between connection and individuality in sustaining healthy family bonds.
Discussion and Conclusions
The findings indicate that love in adult sibling relationships is neither static nor assured; it is shaped by structural changes in the family system. The entry of in-laws is a pivotal transition that can reactivate earlier sibling roles, latent hierarchies, and unresolved emotional patterns rooted in the family of origin. As family boundaries and expectations shift, siblings must renegotiate closeness, loyalty, and limits. In this study, love is conceptualized as a relational experience marked by emotional closeness, belonging, mutual responsibility, and the capacity to sustain connection alongside autonomy.
Drawing on Bowen’s family systems theory, emotional differentiation emerges as a key mechanism explaining divergent sibling outcomes following family expansion. Higher differentiation supports empathy and connection without being overwhelmed by loyalty conflicts, perceived exclusion, or shifting alliances; lower differentiation is more likely to intensify rivalry, distancing, and tension, particularly in contexts of unresolved parental favoritism or rigid sibling hierarchies.
Importantly, the integrated quantitative and qualitative findings suggest that in-law entry does not inherently weaken sibling bonds. Rather, it functions as a relational test that can destabilize patterns or facilitate growth. When siblings tolerate ambiguity and difference, expansion may promote flexible boundaries, improved communication, and an expanded sense of belonging. These insights extend love research beyond romantic and parental ties and highlight opportunities for therapeutic intervention during family transitions.
References
Bedford, V. H. (1992). Memories of parental favoritism and the quality of parent–child ties in adulthood. Journal of Gerontology, 47(4), S149–S155.
Bowen, M. (1978). Family therapy in clinical practice. New York, NY: Jason Aronson.
Furman, W., & Buhrmester, D. (1985). Children’s perceptions of personal relationships in their social networks. Developmental Psychology, 21(6), 1016–1024.
Knauth, D. G., & Skowron, E. A. (2004). Psychometric evaluation of the Differentiation of Self Inventory for adolescents. Nursing Research, 53(3), 163–171.
Skowron, E. A., & Friedlander, M. L. (1998). The differentiation of self inventory: Development and initial validation. Journal of Counseling Psychology, 45(3), 235–246.
Velasco, C. M., Mendoza, I. P., Reyes, A. B., San Fernando, C. O., & Union, L. (2019). Assessment, resilience, and approaches on conflict management: The case of Master of Arts in Science Education students. Don Mariano Marcos Memorial State University Journal of Education Research, 3(2), 45–59.
Deering, C. G. (1991). Correlates of sibling jealousy and parental favoritism (Doctoral dissertation). University of Rhode Island.
Key words: sibling relationships; in-laws; emotional differentiation; family systems; conflict resolution