We propose a distributed control law that solves the tracking-in-formation problem for a group of underactuated autonomous marine vehicles interconnected over an undirected graph and subject to inter-agent collision-avoidance and connectivity constraints. The control approach is based on input-output feedback linearization using the so-called hand-position point as the output. Moreover, the control strategy is able to deal with limited knowledge on the target's state and dynamics as well as with disturbances in the form of unknown irrotational ocean currents. We establish almost-everywhere uniform asymptotic stability of the output dynamics with guaranteed respect of the inter-agent constraints. A numerical simulation illustrates the effectiveness of the proposed approach.