Greetings,
You could install the game from the discs and that would work fine. We also have 2 different online installers available. I have included links to both of those programs below:
Station Launcher: http://launcher.station.sony.com/
Everquest 2 Launchpad: http://everquest2.com/install
If you have characters on both the EU and US servers then you can switch between them using the region select option. If you have plenty of space on your hard drive then you could even copy your Everquest 2 folder so that you have 2 copies of the game on your hard drive. You could then set one to run the US client and the other to run the EU client.
If you want to play all of those characters on the same server then the only real option is the character transfer service. Please keep in mind that the transfer service has a charge of $50 per character.