Depending on the sociological approach, the definition of a family will be difference.
A macro approach would examine the relationship between a family and wider society. Macro sociologists will define a family by its impact on wider society. For example, Durkheim would argue that a family is a stabilizing force in wider society. A micro approach would look more closely at the power relations and dynamics within a family. They might deduce that a family is defined by the relationships between those within the family. A meso approach concerns itself with the sociology of mate selection. A meso-level approach may determine that a family is defined by the romantic relationship between two individuals.
[P1] Families appear different when examining them through a macro, micro, or meso lens. [P2] Any sociological definition of a family can only convey one sociological approach. [P3] Therefore, it is impossible to have just one sociological definition.