Permissions Problem on Shared Calendar - users under same account cannot modify each others appointm

[Paul]

In my organisation we have a number of shared calendars for resources such
as meeting rooms (permissions are set so that users can only modify their
own appointments).

There are two users who job share and who log on with different windows
accounts but the same outlook account. If one user creates an appointment
the second cannot delete or modify it.

Why is this when both users are on the same outlook account?

Is there anything we can do (short of granting permission for these users to
modify any appointment which is unacceptable) to all one user to modify an
appointment created by the other?

TIA
Paul