Coordinated control of marine vehicles poses challenging problems, among them the possibility to use the vehicles, in addition to their nominal mission, also to achieve a relative localization task. To the purpose, the use of a surface, GPS-equipped, vehicle and one or several underwater vehicles may be envisaged. The latters can communicate among them by acoustic modems; those devices can also be used as ranging measurement units thus providing an additional information that, together with the common sensor equipment for marine vehicles, might be used for relative localization. This paper investigates how the vehicles' movements can be commanded in order to help the relative localization by a proper analysis of the system observability and a corresponding proper definition of the vehicles movements; critical situations for the relative observability, that corresponds to common movements, are then avoided. Numerical simulations on the mathematical model of the Fòlaga hybrid underwater vehicle confirm the effectiveness of the proposed coordinated behavioral approach.