The iPad cannot AirPlay to multiple Apple TV devices or iPad devices at the same time. If you want your presentation to appear on multiple screens you may want to look into getting a switcher. This will allow you to AirPlay to an Apple TV, and the output of the Apple TV is connected to the input of a switcher using an HDMI cable, and the multiple outputs from the switcher are connected to multiple TVs using HDMI cables.
There are some limitations as to the maximum length of an HDMI cable (maybe 50 feet) but this setup is used by other customers. You could also send the signal from the iPad directly to the switcher (not using an Apple TV) using an HDMI cable and the appropriate adapter but this would mean being physically tethered to the switcher.