When boxing with different classes, you can't think about it as 'key 1 casts this spell'. You have to think of it as 'key one is my spam button'. Now, what spell do you want the rogue to spam? Which one do you want the priest to spam? Now you know what to put on your 'spam' button. You might even want to use /castsequence to SS 5 times then Evis on the rogue.

For healing, you will want a macro (/cast [target=Rogue'sName] Lesser Heal) and put the macro on the 'heal the rogue' key.

While you can multibox without macros, it is much easier if you take the time to learn and use them.