Since the number of users are not many people can cause them to VPN connect to the PC that stores the database containing the tables. The linked tables in the database that contains the application (forms, reports, etc) are linked as if they were working on a LAN.
Should be optimized bandwidth, ensuring that users have access application forms and work right through consultations, for example to make the form is open to add data, or if you need to work with a data set in place controls restrict the form and then by a button or something similar charge filled the form's record source query by limiting the information in accordance with the provisions. In this way which ensures that data is to be sent from the server and from version to access the tables as low as possible.
The other option is to set up a web server to which you can use Apache, it is very likely to have to migrate the database tables to MySQL or SQL Server (express version is free) and away from here may set the forms in PHP. There are applications that make the Access to PHP though often then must make adjustments.