Background We explored the relationship between family members and healthcare professionals (HCPs), specifically how family members can influence the course and outcome of patient care for youth. Exploring this under-researched area provided an opportunity to understand the tripartite relationship between the family, the youth experiencing mental health problems or substance use concerns and their HCP. Methods A qualitative research design was used to gain a full understanding of how family members experience relationships with HCPs. We interviewed 21 family members using semi-structure questions to explore the type of relationships formed between HCPs and family members throughout a patient’s course of care, the family member’s perceived role in the care of their youth accessing mental health or addiction services and the family member’s awareness of formalized structures (i.e., hospital rules, policies) and resources that support family involvement. Results Within a relationship-centred framework, four themes, with various sub-themes emerged from the interviews: 1) The family member–HCP relationship regarding creating a positive impression, being an extension of the patient and the discovery of “pink flags”; 2) The family member–youth–HCP relationship regarding the receptivity of youth to family involvement and a youth’s individual right to privacy; 3)The family member’s relationship to self with regard to the situation being a family illness; and 4) The family member’s relationship with friends, family and peers regarding the feelings of loneliness, stigma and shame and the lack of understanding about mental health problems and substance use. Conclusions Our study provided in-depth information about the importance of family involvement in the care and health outcomes of youth who are accessing mental health and addiction services. Family members experienced and conceptualized their relationships with HCPs, their youth, themselves and their friends and peers as active interactions that influenced the course and outcomes of care. Future studies are needed to collect the multiple perspectives of youth and HCPs alongside with the family perspectives.