So what about Karl's brother?

Emperor Karl of Austria's younger brother, Archduke Maximilian, was destined for a much more quiet life than his elder brother.  During the first world war, he served in the Austrian army.  In June 1918, Maximilian "led an Austrian battalion against Italian positions on Dorso Alto Mountain," according to his obituary, published in the New York Times.  His troops captured the ridge, but he suffered a serious injury when a "bursting shell shattered his eardrums, and caused a condition of deafness.

Maximilian was promoted and decorated for his success.  Later in the month, his brother, Emperor Karl, decorated him with the Grand Cross of the Order of Leopold for his capture of Fossalta.

But the successes were for naught.  Five months later, on the eve of the Armistice, orders were issued for Maximilian's arrest, but he had already fled the country. At a meeting of Austrian monarchists in Vienna in December 1918, Maximilian "was nominated as successor to the crown."  The socialists, in a dispatch from Vienna, made it clear that they intended to "take sharp measures against monarchists.
In April 1919, Maximilian joined other members of the family in Switzerland.  Later he and his family lived in Bavaria.  By 1923, he was a practicing veterinarian in Switzerland, "having taken the highest degrees in his science," according to a report in the New York Times by Frederick Cunliffe-Owen in 1923.

In 1933, he received permission to live in Austria, the first male member of the family "to be allowed to return.

In 1917, he married Princess Franziska zu Hohenlohe-Waldenburg-Schillingsfurst.  They had two sons, Archduke Ferdinand and Archduke Heinrich.  Their engagement was announced in June 1917. The princess' father was the former Governor of Trieste.

The couple were married at Laxenburg on November 29, 1917.

In later years, Maximilian, who used the title Count Kyburg, lived in a hotel in Nice, France.  He died of a heart attack there on January 17, 1952. (His obituary was published in the New York Times on January 19, 1952, which means the story was written on the 18th, and in the body of the story, it says he died "yesterday, which would indicate the 17th.)     He was 56 years old.

 Archduchess Franziska died at Salzburg  on July 12, 1989.