Custom model of rigidly attached drones in SITL simulation


I am new to ROS, Gazebo and PX4. I am interested in using PX4 with a companion computer (ODROID) on multiple quadcopters.

First of all, I have completed the offboard example which you can find here. Then, I extended it and I am now able to control two drones separately by using PX4 SITL and mavros. Now I would like to have a simulation in which the two drones are rigidly attached together. As a first thing I would like to make them hover and then fly from A to B. How could I proceed to achieve this goal? I am trying to produce a custom drone model of two drones which are rigidly attached in Gazebo. However, I’ve not yet found out the way to produce the wanted drone model.

Can anyone advice me on how to rigidly attach two drones using Gazebo(7.0), ROS kinetic and PX4?

Thanks in advance.