you have 2 choices:

Keyclone - $20 - superb software, does everything you could want and some things you never even knew you wanted. Designed specificaly to multibox and keeps in line with blizzards TOS / EULA

Auto hot keys - FREE - pain in the arse to sort out, as it runs on a user written script could be used to do things that dont comply with blizzards TOS / EULA like pressing multiple buttons on each char not just 1.


Go for keyclone you wont regret it