Family members are important providers of care for older people. In residential long-term care, however, their role is not always simple and straightforward: responsibility for care provision rests officially with staff members, but in practice family members often contribute to providing care. The main reason for admission to long-term care is functional decline. At the same time, the maintenance of functional ability is a central goal in long-term care. It is therefore reasonable to assume that functional ability is also an important factor in the relationship between family members and long-term care residents. This study aims to explore how family members experience their role in supporting the functional ability of older relatives in residential long-term care. With the approval of the local hospital district's ethics committee, we conducted semi-structured interviews with family members (n = 16) in Finland in 2016. Thematic data analysis showed that family members supported the functional ability of their older parent or spouse by organising and monitoring care and by bringing forth their relative's personal needs and wishes. They often saw their role alongside staff members as ambiguous, and their understanding of the scope of support for functioning extended beyond physical everyday tasks. In their talk, family members broadened the concept of functional ability from daily chores and independence to meaningful social relations and acknowledgement of person's individual background and preferences. Family members’ views offer valuable insights into residents’ personal needs, values and preferences and in doing so help care workers to support their functional ability with a person-centred care approach.