You want a Kiosk app.
They restrict the device to just a handful of apps the device administrator chooses and nothing else is accessible without a master password.
Odds are you are going to have to buy the Kiosk app as they are very specialized and free versions are limited, create a single ”corporate” Google account if you will and you then can install the app on a small fleet of devices using the same Google account as your team grows.
If you grow beyond a handful of devices you should consider making a donation to the dev or make sure you fall within the desired limits of the software in regards to licensing, share the monetary love if you will.
Search kiosk in the play store, you will come across many, always try the ones with a free version first as it will give you an idea of what you are looking for.