You need a copy of SPYMONITOR-LOCAL per computer. If you want to use two base stations on the same computer you only need 1 copy of SPYMONITOR-LOCAL, If using two computers 2 copies are required.

The standard copy allows 1 user per project, and you can have up to 16 transmitters per project. But there is no limit on the number of project you can create, but they will all have a single users.

It is possible to have both base stations send to the same project, but you can only use each transmitter ID (between 0 and 15) once.
   
If you plan to put both base stations on the same computer and separate projects, then you will have 1 user per project as standard.
   
Additional user licenses are added on a by project basis, and are locked to the project name.
   
If you plan to send email alarms and reports to multiple users then you might need additional users.