Let me try to understand:

I have a QBDT-Premier (license # ABC. This license is for 2 users: ABC-1, ABC-2). I set up user # 1  as my server and user # 2 as another workstation . Now my accountant also has QBDT-Premier (license # KLM. This license is also for 2 users: KLM-1, KLM-2).

I would like to know can all 4 users (ABC-1, ABC-2, KLM-1, KLM-2) simultaneously work on any file created by either ABC or KLM?

According QB-tech support only users of ABC can work in the multi-user environment