You're doing two different things, pvp and pve. Here's the pve version:

target a mob with main
target main with alts
Bind a different key for each alt that does this:
/focus [target=targettarget]
switch main target
use focus macro
switch main target
use focus macro
switch main target
use focus macro
switch main target
use focus macro
another macro for attacking, it's the same for all of them:
/petattack focus or target (unclear on this part, i don't play pet classes with any macros that don't attack my current target)
/cast [target=focus,exist] [target=target] dot dot dot dot dot drain drain drain


That kind of setup should let you pick 4 different targets, set them as your focus, send in a pet, dot them, then drain tank them all. The focus,exist condition makes sure if you do have a focus you'll attack that, and if not, whatever you have targeted will be attacked instead.

Edit note: You're basically looking to do something similar to a mage polylmorph focus macro or a priest focus shackle macro, but you'll just have to use your main to set focus off of or individually click their target to set focus via macro.

Edit again: You could bang all 4 buttons at one time to set them all to the same target, which takes care of all your non-pvp requirements.