@Ranjeet If you search for jinja in google, you will be able to find the documentation of the jinja templates: Jinja — Jinja Documentation (2.11.x)
It is a templating tool to generate sdf files. As I mentioned in Cannot launch iris_fpv_cam - #2 by Jaeyoung-Lim already, the iris_fpv_cam is not expected to work with the multi_uav_mavros_sitl.launch file. (This is not a bug)
You can either try to generate your own model templates by looking at how it is done in PX4-Autopilot/gazebo_sitl_multiple_run.sh at ed0fa99198c276760f0c7d4e9444492c978a2b00 · PX4/PX4-Autopilot · GitHub