We deal with the control of two robot manipulators carrying an unknown object. We consider the uncertainties in mass, inertia and center of mass of the object. A dynamic model is obtained for the combined system. An adaptive scheme is proposed to track the desired motion trajectory of the object in the presence of uncertainties. A feedforward plus PI type force controller is designed for internal force control. A Lyapunov based stability analysis is conducted for the proposed scheme. In the adaptive motion control scheme for the combined system we cannot specify the individual torques of the manipulators uniquely. To obtain a set of individual torques an optimal control problem is formulated by minimizing a cost function.