Well I think your problems come more from the fact, that you are a fresh learning multiboxer, than from HKN, but here my advice:

1. For activation abilities (like Frostbolt), the most common concept to activate them is to bind them to a key in wow on bothe mages (lets say '2') and simply press that key. You could also do it via mouse broadcasting (as you tried), but I would advise against it.

2. For standing next to each other:
Your normal movements will be done by '/follow' your main mage, so normaly, the main mage will stand infornt of the scond mage.
What you can do, to get them to stand beside each other:
-Create a key, which lets the main-mage walk backwards, and the secondmage move to the left (or right).

This could be done like this (assuming you have bound forward/backwards, strafe-left/right to the arrow-keys):
Code:
<MovementHotkey shift F> 	
         	<SendLabel w1> <Key Down>
         	<SendLabel w2> <Key Left>
now, when you press 'Shift +F' your chars move, and when you stop this at the exact time they form a line.