3 Calibres is not a great way to work with a single book.
You can use the VIEWER part of Calibre without adding the book to the local (portable/not main device)
Consider using the Content server (runs on the main PC). Recent (Calibre 4?) changes allow for additions from Allowed users. The PC does need to remain ON and accessible (router pinhole configured) from the LAN.
For off line use, just download a copy and use a viewer app (annotations will not be 2 way or possible with 3rd party aps)