@AnRuaRi: Unfortunately, such a configuration is not supported out of the box. Insync is a per user program and needs to be installed for every user & two Insync instances should not point to the same physical folder. Insync doesn’t have the capability to match the existing files & hence one Insync instance would consider the files added by the other Insync instance as new. This leads to duplication as you have experienced. So, the solution is to run only one Insync instance and set its folder on the central shared storage.
Please see this workaround to run Windows program as a service: How to run Insync as a service on Windows Server This way Insync runs without requiring you to actively login. However, running as a service means that you cannot access it via UI - you will have to stop the service and start Insync as a normal program to interact with it.
Thanks