You can only use the same login database without conflicting with the other server. This means you can login with the same account info in server A, but different characters. To do this:
Copy your SERVER-A files to make SERVER-B files.
Make a new SERVER-B database(not necessarily a SERVER-A database copy, you can just make a new one).
In SERVER-B files's "/conf/inter_athena.conf" edit only the following to your SERVER-B database:
MySQL Character server
MySQL Map Server
MySQL Log Database
If you're going to run both servers from the same machine, don't forget to change the ports on SERVER-B files's "/conf/login_athena.conf & char_athena.conf & map_athena.conf" you can just make them all +1
Run SERVER-B and edit the login port in your clientinfo.xml to the same as the port in SERVER-B's login_athena.conf
Login with the same info as in SERVER-A database & Enjoy!