If you are using IS Boxer, don't bother with Focus at all.
Unless you are tracking something with Focus, such as your arena burst target or something you are crowd controlling.

If you were to drag Lightning Bolt, straight from the wow spell book (no macros) for each toon.
And place them all on "1".
When you press "1", with any toon, the others will also press "1".
But they'll auto assist the active toon first.
So without any macros or focus, you have FTL -- all the slaves cast at the same target as the master.

As for Warlock DPS.
It will depend on what the macro is for their attacks.
I'd probably use a "click" for them.
Something like: Immolate - Conflagrate - Chaos Bolt - Incinerate.
Or for Affliction: Curse of the Elements, Haunt, Corruption, Unstable Affliction, Shadow Bolt (not repeating the curse).