D.Afonso VI and D.Pedro II were Kings of Portugal and their sister Catarina was Queen of England
D.José I was king of Portugal and sister D.Maria Barbara was Queen of Spain
D.Miguel was king of Portugal and his sister D.Maria Francisca was de jure Queen of Spain
D.Maria II was Queen of Portugal and her brother D.Pedro II was Emperor of Brazil
D.Luis I king of Portugal and his sister Infanta D.Antónia married to the titular Furst of Hohenzollern-Sigmaringen.
On the descendence of Maria Theresia of Habsburg you have
Emperor Joseph II, brother of Maria Amalia, Duchess of Parma, Leopold II Grand Duke of Tuscany (before succeeding his brother Joseph), Marie Caroline, queen of the Two-Sicilies, Ferdinand Duke of Modena and Marie Antoinette, queen of France.
Among Franz II children:
Marie Louise, Emperess of France, Leopoldine, Emperess of Brazil, Marie Caroline, Queen of Saxony, and Emperor Ferdinand.
And the famous daughters of king Maximilian I of Bavaria:
Charlotte, queen of Wurttemberg and Emperess of Austria
Elisabeth Queen of Prussia
Amalia (twin sister) Queen of Saxony
Maria Anna also Queen of Saxony (naturally not at the same time) and her twin sister
Sophie who might have been Emperess, mother of Franz Josef.
They were sisters to King Ludwig I
The discussion on branching out reminds me: what are the periods in European royal history where you had two or more siblings in the same family simultaneously sitting on thrones? It was a common occurrence in the past -- especially before World War I. But of course, this has become an increasingly rare occurrence in modern history. It's easier to go back in time, through the decades, but I've come up with the following (queens consorts are acceptable) --
1972-1973: Anne-Marie was the exiled queen of Greece, during the first year of her eldest sister's reign as Margrethe II of Denmark, the country's first queen regnant in 600 years. The Greek monarchy was abolished in 1973, two years before Juan Carlos was called to the Spanish throne as king, following the death of Generalissimo Francisco Franco. It was then that King Constantine II's sister Sofia became queen. But that example doesn't count, since their reigns never overlapped.
1964-1993: Baudouin was the king of the Belgians while his sister Josephine-Charlotte was the grand duchess consort of Luxembourg
1993-2000: Josephine-Charlotte was the grand duchess consort of Luxembourg, while her brother Albert II was the king of the Belgians
1913-1918: Kaiser Wilhelm II sat on the German imperial throne, while his sister Sophie was the queen consort of Greece
1881-1894: Dagmar was the empress consort of Russia (Maria Feodorovan), while her brother George I was the king of Greece
1906-1910: George I was the king of Greece while his older brother Frederik VIII was the king of Denmark; also, their sister Alexandra was the queen consort of Great Britain
1910-1936: George V was the king of Great Britain, while his sister Maud was the queen consort of Norway
1912-1947: Christian X was the king of Denmark while his brother Haakon VII was the King of Norway
1894-1917: Ernst was the reigning grand duke of Hesse-Darmstadt while his sister Alix was the empress consort of Russia
1848-1862: Maximilian II was the king of Bavaria, while his brother Otto was the king of Greece
1859-1861: Elisabeth was the empress of Austria-Hungary, while her sister Marie Sophie was the queen of the Two Sicilies
Can anybody fill me in on additional examples within the last 200 years? I'm less familiar with the smaller German houses.