Diego Cortes also is a unfinished (unable to deploy yet) character. He was made as a secret character along with Isaac (your ship's previous captain).
This is the rest of the crew if you follow all side quest and main quest.
Removable character through certain scenarios or if you skip the side quests:
Rylan, Katari, Bradley, Skru'Vaks, Phoenix, Feraldo, Jhaan, Hakkon, Cicero, Alastor, Diego Cortes (still cannot be part of the crew yet W.I.P), Master X (Xperiment-fictional character of the game's author himself), Levi, Asmodeo, Isaac, (Jhaan's and Sammuel's former crew members, unimplemented yet).
Characters that is essential and they cannot be remove in anyway as of this version 43.3:
(Sammuel and Arthur)