We discuss the application of deontic logics to the modelling of variabilities in product family descriptions. Deontic logics make it possible to express concepts like permission and obligation, and hence promise a direct modelling of constraints over the products of a family. Indeed, we first show how feature models can be straightforwardly characterised by means of a deontic logic. We then study the deontic modelling of the behavioural variability in product families by defining a deontic extension of a behavioural logic. This allows both constraints over the products of a family and constraints over their behaviour to be expressed in a single framework: a novelty in the field. We discuss how model-checking tools could support formal verification in this framework, and we indicate some future research into that direction.