You will need new copies of FileMaker at each location in order to upgrade to version 12. It uses a new file format so each file must be converted to the new format.
Do you need to see data from your multiple locations combined in a single report?
Filemaker currently has a buy one get one free promo until Dec 20, 2012
A single database could be hosted by a service for $20 to $50 per month
Each site could host their database for your access - FMP allows nine concurrent users and 5 Instant Web Publishing users
1] This would mean the hosting computer would be on
2] The database would be set to share
3] The local router's port forwarding is setup for remote access
The drawback would be that you would have to view each database rather than a central db
FMP Server is $1000 FMP Server Advanced is $3000
You can not mix FMP ver12 with earlier versions