Previous studies have suggested the impact of intervention fidelity on the management and prevention of chronic diseases; however, little is known about the effect of the contributing determinants (at multiple levels of influence) that can impact health-related interventions intending to improve the health status of Hispanic adolescents with overweight or obesity. The current study aimed to assess whether fidelity (i.e., dosage and quality of the program delivery), acculturation (i.e., orientation to the American culture, retention of Hispanic cultural values), and individual-level socio-demographic characteristics (i.e., income, education) predict changes in family processes (e.g., parent control), which in turn may affect adolescent health-related outcomes including body mass index (BMI), physical activity, dietary intake, and adolescents' health-related quality of life. A pathway analysis model was utilized to explore the study variables among 140 Hispanic parent-adolescent dyads randomized to Familias Unidas Health and Wellness (FUHW) intervention. Results indicated that fidelity was significantly associated with changes in parent-adolescent communication, parent monitoring, limit-setting, and control. Parents' education was associated with changes in parent limit-setting, and parent Hispanicism was associated with changes in parent limit-setting and discipline. The examination between family processes and adolescent health outcomes revealed that parents' higher discipline and improved communication with their adolescents were significantly associated with improved adolescents' quality of life, and parent control was positively associated with physical activity and negatively associated with BMI in adolescents. Our findings demonstrated the significant contribution of intervention fidelity and participants' characteristics in parenting strategies leading to adolescents' health outcomes to prevent obesity-related chronic diseases. Future research is needed to investigate the effect of environmental and organizational factors on the delivery of the intervention materials.