Complex sentence: The new king retained Fielden as Captain of the King's Flight, and his role was expanded to the carriage not only of members of the Royal Family, but also members of the Air Council and other important state personages.
Split into simpler sentences: The new king retained Fielden as Captain of the King's Flight, and his role was expanded. He was charged with the carriage not only of members of the Royal Family, but also members of the Air Council and other important state personages.