to box 2 healers be it kara og 25 mans raid, have to be perhaps the biggest challance a boxer can have.
one ting is healing on two char, another is the be healing the rigth char(s) at the rigth time.
it should not be impossible, but very hard not to mention very quick hands and first class macro config.

if you where to be assigned to "main" heal 2 to 3 targets i can see how multiple flashheal and shield trowing will be a advantage to tosh around when needed.
but hard to put it mildly.

migth be possible to do someting like this
button a
healer 1
target maintank
cast flash 1
button b
target mantank
cast big heal
button c
target maintank
cast renew
button d
target maintank
cast shield



healer 2
button a
target offtank1
cast flash heal
button b
target offtank 1
cast big heal
target offtank 1
cast renew
target offtank 1
cast shield

those you can have on both healers, if you use the numpads to mix the heals up a bite with various other heals and targets and crosshealing
so both are toshing renew on numpad 9 and both are toshing big heal on num pad 8 and crosshealer on numpad 7 so both heal the same other targets.

ok bad explanation but should give you a very rough idea on how to configure this so it have a sligth chance to actually work, but it will be very hard i assume.

if you do try it, please update us on how you did it and how you configured it and if it worked or not

Silver