We started ICC achievement-runs recently and seem to have much trouble in this seemingly easy achievement called Full House: Full House (10 player) - Achievement - World of Warcraft
We start to burn the boss down once all the needed adds are there, but it has happened twice now that once the boss is down, one of the adds were either missing or transformed into another.

I'd want to make a macro that checks if all the mobs are present when needed. I think this could be done with "noexist" script so that if one of the listed mobs is missing I get "X is missing!" - raidwarning.

Mobs I need to track are:

Deformed Fanatic
Reanimated Fanatic
Reanimated Adherent
Cult Fanatic
Cult Adherent

the best I could come up with was this:

Could someone please point me to right direction and help me make this macro work?

It is not possible to target or even check the existance of Mobs with spaces in their name by using a "target="-option in a macro. In addition to that, you can not use macro options with slash commands that produce a chat message, such as /say or /rw.
Due to those two technical limitations it seems to be impossible to have one macro check all of the needed mobs at once, you rather need a seperate "old school" macro for each type of mob.

Just create five different macros, one for each mob:
Lady Deathwhisper only transforms mobs in phase 1 so there should be enough time in phase 2 to click all five macros.
It might also be possible to combine those five macros with /click in a sixth macro but I got absolutely no experience with that command yet.

That would work. Just needed a name in place of %t because there would be no target.

This is what 1 macro to check all 5 would look like, I think. However, it goes over the 255 character limit so you would need a macro extender mod.
You would need an additional 5 macros like this:
They need to be placed on the corresponding buttons. Spots for the above example: http://i53.tinypic.com/2jb79d2.jpg

Making 5 different macros to click is out of the question, but making a separate macro to "click" them all would probably be worth testing. Do you guys know if this will trigger global cd for each of those 5 target macros?

Nope, no GCD. However, you should pause your manual targeting a bit before and after pressing it just to make sure you doesn't mess up the [noexists] checks.