Background: This study examined how siblings and siblings-in-law of persons with intellectual disabilities experience the establishment of and processes within the couple relationship. Method: In-depth semi-structured interviews with 12 siblings and 12 siblings-in-law of persons with intellectual disabilities were analysed using thematic analysis. Results: The participants did not perceive their special siblinghood as detrimental to their couple relationships. Siblings-in-law's prior acquaintance with persons with disabilities and professional support provided to the family of origin emerged as contributing factors. The effect of the siblinghood on the couple relationship was both positive and negative. Conclusions: The findings support the importance of the acceptance of others who are different, including in couple relationships when a sibling or sibling-in-law has intellectual disabilities, and underscore the role of professional therapists.