Siblings of young people with chronic illness commonly undertake caring responsibilities for their affected brother/sister, which may encourage maturation, yet may also be perceived as a burden. Our study determined (1) siblings’ caring responsibilities, (2) siblings’ current emotional distress and psychosocial functioning, and (3) how siblings’ caring responsibilities and psychosocial functioning related to familial relationships and coping strategies. Siblings completed questionnaires which contained Sibling Inventory of Behavior, Sibling Inventory of Differential Experiences, PedsQL, emotion thermometers, Brief COPE, and a checklist of caregiving responsibilities. We analyzed the data with t-tests and multi-level models. Forty-five siblings (mean age = 15.40 years, SD = 3.31 years; 60.0% female) participated. Siblings who had caring responsibilities ( n = 26, 57.8%) reported lower anxiety symptoms, lower need for help, greater use of problem-focused coping, and more companionship and teaching/directiveness with their affected brother/sister than siblings without caring responsibilities. Siblings reported lower psychosocial and physical functioning when they perceived their parents provided them with less affection than their affected brother/sister. Family-based psychosocial interventions may aim to improve the sibling–parent relationship (including expressing affection) and the sibling–sibling relationship. Future interventions may also focus on increasing siblings’ use of problem-focused coping strategies.