In this article, the problem of controlling two interconnected gantry cranes, controlled by two agents sharing no information about their subsystems dynamics while confronting large uncertainties on their own plants, is tackled from the viewpoint of decentralized Active Disturbance Rejection Control (ADRC). The proposed solution is not only robust with respect to static influences caused by the state interactions due to operation of the individual cranes in the tracking of a given cooperative trajectory, but it is also robust with respect to the inclusion of dynamic unknown disturbances represented by an arbitrary number of un-modeled mechanical systems affecting both cranes. The results are illustrated by means of pertinent simulations.