login with one user to a device, which is registered to another domain in another tenant

There are two schools with a tenant each and by intune managed devices, also two different domains.

Goal is

to login with me@school1.de at a device, which is registered at school2.

And vice versa, login with me@school2.de at a device, registered in the school 1 tenant. 

Reason: teachers work in school 1 as well as school2 and do not want to use different logins.

Is there a way to manage this?

Ingo