Caregivers of children with autism spectrum disorder (ASD) experience greater stress, expressed emotion (EE), and affiliate stigma than caregivers of children without ASD. Siblings of children with ASD often experience greater negative functioning than siblings of individuals without ASD. The current study found significant interrelations among symptom severity and externalizing behavior in children with ASD; parental stress, affiliate stigma, and EE; and TD sibling internalizing behavior. In addition, certain subcomponents of affiliate stigma predicted unique variance in EE and TD sibling internalizing behavior. Findings may increase understanding of psychosocial functioning in families with children with ASD and allow clinicians to improve outcomes for all family members. Limitations of the study included self-report data, limited sample diversity, and a cross-sectional design.