Could you just move the media files (including the folder structure) to an identical and simple base path like "C:\music" on all three PCs? It isn't necessary (or in my opinion even recommended) to use the "user's personal folders" concept with large media libraries.
Step by step:
On the "primary computer",
1. Create a fresh library backup file (it's good to have it if something goes wrong)
2. Disable the auto-import feature (untick the "run in background" setting)
3. Move the files and folders outside MC by using Windows Explorer. A simple drag and drop should move the complete file structure quickly if the target location is on the same disk partition.
4. Fix the library to point to this new base path:
- Select all files and open the Rename, Move, & Copy Files tool.
- Select the
Update database point to new location (no file rename, move or copy) option
- Tick
only the
Find & Replace option
- Find what:
C:\Documents and Settings\Owner\My Documents\My Music - Replace with:
C:\Music After you have moved the files also on the other PCs just open MC and restore a new library backup file from the primary computer (create a backup file after the location fix is applied).
The restored library will work on the other PCs as it works on the primary computer. You don't need to import anything. You can keep the auto-import feature disabled on the other PCs if you always first copy the new music files and then restore a new backup file.
EDIT
You didn't mention how you copy the media files from a computer to another, but if you want to keep separate locations synced and don't have a dedicated program for that I can recommend
Karen's Replicator (freeware) or
SyncBackSE (commercial, but not very expensive).