Internet solution, printing problem
If you have the option of buying new printers, you can buy a portable Bluetooth printer for them to use. Using Bluetooth you're no longer dependent on any WiFi, and the iPad can use its WiFi to connect to a guest network for internet access or anything you like.

Using a Bluetooth printer is possible because you have an in-house built app. The app would require slight tweaking to support the printer.

For example you could use the HP PJ-763MFI Bluetooth printer which is created for use over Bluetooth with iOS:

https://www.brother.co.uk/mobile-printers/pocket-jet/pj-763mfi

The HP printer support A4/letter size paper.

Another option for smaller paper sizes are the popular Zebra printers that are certified for use over Bluetooth with iOS:

https://www.zebra.com/us/en/products/printers/mobile/mz-series.html

You can also find similar printers from Star and others.