Sharing Excel sheet over network?
Solution 1:
If you try and access an Excel Spreadsheet (or Access Database) with more than one user you are very likely to run into filesharing or permission issues, I would reccomend using something like MySQL that would support it. You have to bear in mind with Thin Clients that, as they are a stripped-down OS they may not have the drivers for the barcode scanners - there's probably better ways of doing what you want.
Solution 2:
Have you tried using something like Google Docs / Office 365 as either of these two spreadsheet products are designed for collaboration?