Local applications
Everything runs on a single PC. Client, HMI Server, Data Server, and the FT Directory (local). You can have remote OPC Data Servers. But otherwise, everything is on the same PC. If you want to use FT Historian, it also has to be on the same PC.
Network Station
Still just one HMI Server and one HMI client that are on the same PC. They cannot be remote. But you are now using the FT Network Directory so the Data Servers, Historian, and FT Directory can be remote. If you have two separate applications, they can share the Data Servers and Historian and users would be shared as well.
Network Distributed
Clients can now be remote. One applications can have multiple HMI Servers along with multiple Data Servers. All items can be distributed as needed to one or more PCs.
Sounds like you really want a single network distributed application possibly broken up into separate areas. All the clients can then talk to the same application. Plus you don't have two separate applications hitting the data servers for data.
OG