The article looks at the social roles of the sibling and the sibling-inlaw among older adults and how these roles are interconnected. It is based on an analysis of data collected in Czechia in 2017–2019 from 91 qualitative interviews and three focus groups with participants aged 50+. The concept of social roles used here considers a plurality of role repertoires, which actors can choose from, combine, and variously emphasise. Focusing on the social roles of the sibling and the sibling-in-law shows how each of these roles is specific. Both of these roles have a repertoire of targeted support for sibling/ kin cohesiveness and a repertoire of common solidarity and sociability. The sibling‘s role also includes repertoires of intimate closeness and emergency assistance. Both roles can be performed as a minimalist repertoire. The repertoire of the sibling-in-law role is defined in relation to the role of the sibling/ the life partner; the minimum expectation of a sibling is to not avoid contact with others and to show an interest in his/her sibling. Both roles are based on mutual autonomy and at the same time a willingness to maintain the sibling / kin relationship. How the two roles interfere and interact with each other is clear and provides insight into other dimensions of both roles. While it is possible to remain with the minimalist repertoire, it can generally be said that the role of a sibling and the role of a sibling-in-law acquire increasing importance as people grow older.