The active toon, or master, is manually played by you.

The other toons, or slaves, should be on auto follow.
You might break follow, and have a "spread out macro" or such.
But follow will be the default behavior 99% of the time.
You can run a little past the others, and they'll turn to follow, which controls their facing etc.

Then you need a software/hardware option of some sort (I recommend IS Boxer) to "broadcast" to the other clients.
This tells them to kill what your active toon is killing.
When you press 1 on the master, you want the slaves to also press 1, and to cast at your same target.
Same idea for your other DPS keys.