Just create 3 additional database in your current MySQL server and name them likerealmname_auth, realmname_char, realmname_world
Well, I use SQLYog for managing my databases, creating backups, importing/exporting SQL dumps and so on. In SQLYog, you just need to right click into blank place in database tree, select Create Database (ctrl+D btw) and there you go.Fill in name you wish to give to database, charset utf8 and collation utf8_general_ci always worked for me and is used by TC2 by default. Using another settings might sometimes not work properly, but I am not sure about that. Then you will just need to fill that database, so you will most likely import new blizzlike TC2 database. Or you can copy old databases to new ones, so you will have 3 pairs of same databases, but you can modify any of those pairs without modifying 2nd one.Process would be similiar in any other MySQL editor, if you don't want to use SQLYog.
I suppose that actually reading something about MySQL would help you before you start to run multiple realms and such things.
Idk what is "denwer"