My records show no "George" as a son of either Alexander or Gottfried around the year 1787, and especially with a last name of "Diffendaffer." All the offspring in that period were either "Diefenderfer" or "Dieffenderfer."
I find a George Diffenderfer, son of Johann Jacob Dieffenderfer, born 1755, and a George Diefenderfer, son of Philip Diefenderfer, born after 1785, but they are obviously not what you are looking for.
There is an Alexander Diefenderfer, son of Johann Alexander Dubendorger (one of the two brothers who came from Germany) amd Gertride (?). JAD's third wife. Alexander married Elizabeth Leydich, but I have no record of their offspring.