no they cant. when 1 priest is healing the unit, the other priest would just stand there. well, you can equip the prist with another healing ability like Essence of Blight, just make the target number to 1. or just make the priest healing ability shorter cooldown.
if you can't, you could do it with triggers
make a dummy ability that does nothing and create a trigger
Code:
Event
A unit starts the effect of a ability
Condition
Ability being cast equal to <your dummy ability>
Actions
Set life of target unit of ability being cast to current life of target unit of ability being cast + <how much healed>
it might not work, i didn't test this but it might be worth a try
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.