You've mentioned that they each have their own machines, but if they need to log onto a co-workers machine, and then use the file, saving it through "C:\Users\Public\Desktop\" will make it available to different usernames.
Public Sub SaveToDesktop()
ThisWorkbook.SaveAs Filename:="C:\Users\Public\Desktop\" & ThisWorkbook.Name & "_copy", _
FileFormat:=xlOpenXMLWorkbookMacroEnabled
End Sub
I'm not sure whether this would be a requirement, but may help!