That sounds much more like a system security request, more than an excel request. Once someone has created the files A, B & C. They need to be placed into specific network forlders, then they set permissions based on the location of the staff.
The other option would be to create the spreadsheets they way you want, then add passwords to make modifications to the sheets you want to protect. You only make available the passwords to the file A to site A, file B to site B, file C to site C.
I hope that helps.