Arming multiple quadrotors in Gazebo Classic SITL

I am trying to set up a multiple vehicle controller with ROS noetic using Gazebo, but I have run into a roadblock with initializing multiple drones in simulation. I am using c++ to create the code.

I have modified the the mavros offboard example (MAVROS Offboard control example | PX4 User Guide) to suit my needs up until this point, but I am unable to have multiple drones arm and fly in the same simulation instance.

For starters, the main function looks like this:

int main(int argc, char **argv){  
    waypoint way_point;

    ros::init(argc, argv, "five_move_sim_node");
    
    ros::NodeHandle nh;
  
    ros::Subscriber state_sub = nh.subscribe<mavros_msgs::State>
        ("uav1/mavros/state", 10, state_cb);
    ros::ServiceClient arming_client = nh.serviceClient<mavros_msgs::CommandBool>
        ("uav1/mavros/cmd/arming");
    ros::ServiceClient set_mode_client = nh.serviceClient<mavros_msgs::SetMode>
        ("uav1/mavros/set_mode");

    //the setpoint publishing rate MUST be faster than 2Hz
    ros::Rate rate(20.0);
  
    // wait for FCU connection
    while(ros::ok() && !current_state.connected){
        ros::spinOnce();
        rate.sleep();
    }
    
    mavros_msgs::SetMode offb_set_mode;
    offb_set_mode.request.custom_mode = "OFFBOARD";
  
    mavros_msgs::CommandBool arm_cmd;
    arm_cmd.request.value = true;
  
    ros::Time last_request = ros::Time::now();
    
    while(ros::ok()){
        
        if( current_state.mode != "OFFBOARD" && (ros::Time::now() - last_request > ros::Duration(6.0))){
            if( set_mode_client.call(offb_set_mode) && offb_set_mode.response.mode_sent){
                ROS_INFO("Offboard enabled");
            }
            last_request = ros::Time::now();
        } else {
            if( !current_state.armed && (ros::Time::now() - last_request > ros::Duration(6.0))){
                if( arming_client.call(arm_cmd) && arm_cmd.response.success){
                    ROS_INFO("Vehicle armed");
                }
                last_request = ros::Time::now();
            }
        }
    
        way_point.go_to_skyhome();
  
        ros::spinOnce();
        rate.sleep();
    } 
    return 0;
}

I can swap the ROS topics “uav1/mavros/state” etc with “uav0/mavros/state” but this only arms and flies one drone. I have tried to mimic this code in a function that is called for in main(), but it is never able to arm or offboard the vehicles. This code I have shared works on individual drones, so it is not an issue with the way_point.go_to_skyghome() function that sends setpoint commands. I have also tried to search for the specific instances of “mavros_msgs::SetMode” and “mavros_msgs::CommandBool” but I cannot find any documentation on how to extend these to multiple drones.

I found on the forums a post by user Jaeyoung-Lim GitHub - Jaeyoung-Lim/mavros_swarm: ROS based mav fleet control for swarming but I cannot see any commands that arm the drones.

Is there a better method in c++ to arming and offboarding multiple drones for flight in a single simulation environment? What code should I use instead to arm and offboard the drones?