Given the new T-Shirts being Zombie/Reanimator themed I've got a theory.
Copia- Pestilence ( Due to his fondness of Rats and the gas mask themed Ghoul attire. Also could be 'Copy' )
Imperator- War ( Her name means Commander, you could say she waged war against the church by orchestrating the death of it's Papas )
Mr. Sultarian- Famine ( Name could also be translated to Famine, asked if he 'likes food' and his only comment is that he can smell it. )
Papa Nihil- Death ( Fucking Died. Skeleton paint on face. Nihil also just means Nothing which can be equated to death. )
Little Rat Man and his Mamma are gonna revive Nihil to bring about the Apocalypse.