Background: Supporting an adult with autism spectrum disorder (ASD) can be associated with family stress but also with personal growth and resilience. Research providing insight into how typically developing siblings make sense of their unique sibling relationships in adulthood remains limited. Method: Using interpretative phenomenological analysis, this study explored subjective experiences of eight siblings of adults with ASD and co-occurring intellectual disability. Results: Analysis of interview transcripts revealed a complex lived experience explained by the overarching theme "engaging with and navigating limbo," which was characterized by commitment to the sibling relationship, power tensions in the family, uncertainty about the future and negotiating the tension between relational closeness and distance. Conclusion: Using family systems theory, overregulation and closed communication emerged as processes relevant to families living with ASD. Clinical opportunities to support family communication, change tolerance and belonging are discussed.