iPads stuck in Guided Access Mode
Looks like your devices are in Single App Mode- different from Guided Access. This is enabled through Apple Configurator or an MDM solution. To exit, connect the device to a Mac with Apple Configurator 2 installed. Then, select the device and the Actions menu (in the menu bar) select Advanced - Stop Single App Mode. 

To re-enable kiosk mode, simply follow the same process, instead selecting Start Single App Mode.

Note: If Single App Mode was started using a configuration profile or MDM, you'll need to remove the profile, which can be done by selecting Actions - Remove - Profiles...