Hebrew was the only language that any of the disciples could speak. Aramaic was the language of the descendents of Shem’s eldest son Aram, and spoken by the upper classes of Babylon, but never was used by any of the Hebrews that exited Babylon, although they did add aramaic words that had no counterpart in Hebrew to their vocabulary.
It is utterly illogical to think that the original manuscripts of NT books were written in anything but Hebrew. Who would have educated the disciples to write that language?
What evidence do you have that the Gospel authors did not have familiarity in Greek as well as Hebrew?