sluke Basically we want the teachers working in the LAN-based environment to have access to the same content as teachers accessing in internet-connected schools.
This is totally feasible, e.g. it is done with MoodleBoxes in France, several penitentiary centres, to enable prisoners to follow University courses with no Internet connection. See https://moodlebox.net/en/news/caen-detention-centre/.
The idea is to export the Moodle courses from the "central" Moodle, and to import them in the "remote" one, taking care of the logins. If the "remote" platform is not connected to the Internet, you won't be able to use SSO.