coexecutor

from The Collaborative International Dictionary of English v.0.48

Coexecutor \Co`ex*ec"u*tor\, n.
   A joint executor.
   [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

CO-EXECUTOR. One who is executor of a will in company with another. In 
general each co-executor has the full power over the personal estate of the 
testator, that all the executors have jointly. Vide Joint Executors. But one 
cannot bring suit without joining with the others.