Extended longevity among adults with Intellectual Disabilities (ID) and increasing rates of diagnosis of Autism Spectrum Disorders (ASD) mean that parents are unlikely to remain primary carers throughout the lifecourse of adults with ID and ASD. In the context of decreased funding for disability services and policy moves toward de-congregated living, non-disabled (ND) siblings of people with ID/ASD are increasingly likely to be drawn into support and care roles for their siblings. Drawing on literature on moral emotions and the ethics of care, and on narratives collected from 25 ND siblings in Ireland in 2015/6, this paper explores the emotional dynamics entwined in the care and support roles ND siblings engage in. Findings indicate that relationships forged in childhood underpinned the moral ethic to care exhibited by many participants and that their caregiving was experienced as moral practice and emotional engagement, shaped by and constitutive of biography and moral identity. When making care choices, siblings undertook evaluative judgement of their own behaviours, which was informed by perceptions about obligations to care and about what constitutes good care. Decisions about care had emotional resonance, with guilt, other-oriented empathy and righteous-anger emerging as the key emotions in the narratives. Dilemmas between autonomy and relatedness caused siblings to grapple with feelings of resentment and guilt, and many struggled to exercise self-compassion in the face of perceived moral failings. Others experienced conflict characterised by a struggle to reconcile competing care and nurturing expectations within their intimate relationships. Through ongoing self-evaluation of their care behaviours siblings' moral identities were continually reconstituted. It is imperative that service providers and professionals understand and acknowledge such moral and emotional dynamics when working with people with ID/ASD and their families.