You basically have two options:
- set up a server in each office and sync between the servers
Pro: very fast connectivity for the people in each office
Con: need very stable sync solution
- set up one central server and everybody works against that one server
Pro: no syncing
Con: potentially slow connectivity speeds
The other consideration is whether there is need for the remote people to work in areas that they have no connectivity whatsoever so that their only choice is to work with the database locally and then sync when they can.