William Henry, Prince of Nassau-Usingen
Prince William Henry of Nassau- Usingen( born 2 May 1684 in's- Hertogenbosch; died: 14 February 1718 in Usingen) was from 1702 to 1718 Prince of Nassau- Usingen.
Charles Émile Troisier
Charles Émile Troisier( 6 April 1844 – 11 December 1919) was a French surgeon.
Princess Charlotte Amalie of Nassau-Dillenburg
Charlotte Amalia of Nassau- Dillenburg( 1680 in Dillenburg – 1738) was a German regent; regent of Nassau- Usingen from 1718- 1732.
She was a daughter of Prince Henry of Nassau- Dillenburg and Dorothea Elisabeth, a daughter of George III of Brieg.
In 1706 in Dillenburg, she married Prince William Henry of Nassau- Usingen.
The couple had ten children; the first child was born on 3 April 1707 and the last one on 6 March 1718.
William Henry died in 1718, and Charlotte Amalia became regent for her underage son Charles.
Charles William, Prince of Nassau-Usingen
Charles William( 9 November 1735 – 17 May 1803) was Prince of Nassau- Usingen from 1775 until his death.
From 1797 until his death, he was also titular Prince of Nassau- Saarbrücken, however, Nassau- Saarbrücken was occupied by France during that period.
He was born in Usingen, the eldest son of Prince Charles of Nassau- Usingen and his wife, Christina Wilhelmina, the daughter of Duke John William III of Saxe- Eisenach.
In 1770, Charles William became Lieutenant- General in the Dutch army.
In 1789, he was promoted to general and in 1790 to colonel of the Walloon regiment and captain of the grenadiers.
In 1775, he succeeded his father as Prince of Nassau- Usingen.
In 1783, he concluded a treaty of inheritance with the princes of Nassau- Saarbrücken, Nassau- Weilburg and Nassau- Dietz( i.e., Orange- Nassau), in which it was agreed that the Nassau lands were indivisible and that mutual succession among the various branches based on primogeniture would be observed.
In 1797, Prince Henry Louis of Nassau- Saarbrücken died childless and Charles William inherited his principality.
However, under the Treaty of Lunéville, the territories on the left bank of the Rhine were lost to France.
The Reichsdeputationshauptschluss of 1803 compensated Charles William with territories taken from the Electorate of Mainz, the Electorate of Cologne, Electorate of the Palatinate and Hesse.
Charles William died later that year.
Since he had no male heir, he was succeeded by his younger brother Frederick Augustus.
Walrad, Prince of Nassau-Usingen
Walrad Usingen of Nassau( 25 February 1635 in Roermond – 17 October 1702 in Usingen), was from 1659 Count, and from 1688 Prince of Nassau- Usingen and founder of Usingen line of the House of Nassau.
Elisabeth of Nassau-Dillenburg, Countess of Wied
Elisabeth of Nassau-Dillenburg (1 December 1488 – 3 June 1559 in Dillenburg) was a member of the House of Nassau.
She was a daughter of John V of Nassau-Dillenburg and his wife Elisabeth of Hesse-Marburg.
Her brothers were Henry III of Nassau-Breda, John of Nassau-Vianden-Dietz, Ernest of Nassau and William the Rich.
Her sister was Maria of Nassau.
Charles, Prince of Nassau-Usingen
Charles, Prince of Nassau- Usingen( 31 December 1712 – 21 June 1775), was from 1718 to 1775 Prince of Nassau- Usingen.
Frederick Augustus, Duke of Nassau
Friedrich August, Duke of Nassau, Prince of Nassau- Usingen( 23 April 1738 in Usingen – 24 March 1816 in Wiesbaden) was the last Prince of Nassau- Usingen and, jointly with his cousin, Friedrich Wilhelm of Nassau- Weilburg, first Duke of Nassau.
He died without surviving male issue and was succeeded by his cousin's son, Wilhelm.
Princess Caroline of Nassau-Usingen
Princess Caroline of Nassau- Usingen( 4 April 176217 August 1823) was the elder daughter of Karl Wilhelm, Prince of Nassau- Usingen, and wife of Landgrave Frederick of Hesse- Kassel.
Frederick William, Prince of Nassau-Weilburg
Frederick William, Prince of Nassau- Weilburg( 25 October 1768, The Hague – 9 January 1816, Weilburg) was a ruler of Nassau- Weilburg.
In 1806 he was given the title of Prince of Nassau, while his cousin, Prince Frederick Augustus of Nassau- Usingen, became the Duke of Nassau.
Frederick William died in January 1816, only two months before his cousin.
Both men were succeeded by Frederick William's son, William.

Question: Who is older, Charles, Prince Of Nassau-Usingen or Charles Émile Troisier?
Answer: Charles, Prince Of Nassau-Usingen