Complex sentence: In 1917, Emperor Charles of Austria granted Francis Ferdinand and Sophie's eldest son the title of "Duke" with the style of Highness, the other members of the family remaining titled "Prince" or "Princess" with the lesser style of Serene Highness.
Split into simpler sentences: In 1917, Emperor Charles of Austria granted the eldest son of Francis Ferdinand and Sophie the title of "Duke" with the style of Highness. The other members of the family retained the titles of "Prince" or "Princess" with the lesser style of Serene Highness.