Joint the sdf model

I want to make a Multi-Vehicle simulation with Gazebo for three X500 Quadrotors. And I want two rope links between the payload and the two Quadrotors. Should I use the Multi-Vehicle simulation in the docs to name each of the two rotors and joint the sdf model of the rope with the payload(how to do that, or should I write the two rotor models and the model of the rope with the payload to a single sdf file. If the load is too large to send takeoff command quadrotors can not fly to the target point, how to modify and their own sdf model corresponding to the force of the motor to make the quadrotors fly. Thank you for your responce.