Louis Bonaparte himself was King of Holland between 1806 and 1810. He abdicated in favour of his oldest remaining son Louis II (who was king for less than two weeks). The youngest son Charles Louis Napoleon became Napoleon III of France.
I missed Frederik VIII of Denmark father of Haakon VII of Norway (his second son Carl) and Christian X of Denmark.
France and Spain had multiple brothers becoming king.
Francois II, Charles IX and Henri III all three sons of Henri II.
Louis Ferdinand, dauphin of Louis XV had Louis XVI, Louis XVIII and Charles X.
Felipe V of Spain had his sons Luiz I, Fernando VI and Charles III all in Spain. Charles had been kIng of Napels and Sicily as well and was succeeded there by his younger son. Infante Felipe became the Duke of Parma and Piacenza and two sisters became Queen of Portugal (Marianna Victoria) and Queen of Sardinia (Maria Antonia). Maria Raphaella was the first wife of Louis XV's dauphin but died shortly after giving birth to their only child, a daughter.
I was wondering about the last royal in each house who was the parent of two or more persons who sat on thrones -- whether as reigning monarchs or consorts. This is an increasingly unlikely event in the future, so as I was interested in past history.
UK: King George V was the father of two kings, Edward VIII and George VI
Norway: none since the country gained full autonomy in 1905
Denmark: King Frederik IX was the father of two queens, one regnant (the present Margrethe II) and one consort (Anne-Marie, wife of the deposed King Constantine II of the Hellenes)
Sweden: King Oscar I was the father of two kings (thanks to the Salic law) -- Carl XV and Oscar II. King Gustaf VI Adolf (father of Queen Ingrid of Dennark) would hold this distinction, had his eldest son survived to succeed him on the Swedish throne. As it was, the then-hereditary prince (eldest son of the then crown prince) died tragically in a plane crash in 1947. Also, Prince Carl (second son of King Oscar II) could have been the father of two queens. As it was, his daughter Martha died before her husband's accession to the Norwegian throne as King Olaf V.
The Netherlands: King Willem II was the father of King Willem III of the Netherlands and the Grand Duchess Sophie of Saxe-Weimar-Eisenach.
Belgium: King Leopold III was the father of Kings Baudouin and Albert II, as well as the Grand Duchess Josephine-Charlotte of Luxembourg
Luxembourg: Grand Duke Guillaume IV was the father of the Grand Duchesses Marie-Adelaide and Charlotte.
Liechtenstein: Prince Aloys II was the father of Princes Johann II and Franz I.
Spain: I believe it was King Carlos IV, the father of King Fernando VII and several daughters who became queens
Monaco: can anybody fill me in on this?
As for non-reigning houses: I believe Czar Alexander III of Russia could count, since his son Michael technically succeeded to the throne after the abdication of Czar Nicholas II.
In Greece, King Paul was the father of King Constantine II of the Hellenes and Queen Sofia of Spain.
Romania: King Ferdinand was the father of King Carol II of Romania, Queen Elisabeth of Greece, and Queen Marie of Yugoslavia
Bulgaria: none that I'm aware of
Yugoslavia: none that I'm aware of
Albania: none that I'm aware of
Montenegro: none that I'm aware of
Portugal: I'm not sure if King Carlos I would qualify as the father of two kings, since succession was not automatic in the country. His elder son and heir apparent, Prince Royal Luis Filipe, was assassinated alongside him -- and I believe survived him by 20 minutes. But he is not recorded in history as having technically been king during that time ... As for before, can anybody fill me in?
Italy: King Vittorio Emanuele III was the father of King Umberto II of Italy and Queen Ioanna of the Bulgarians
Austria: Emperor Franz I was the father of Emperor Ferdinand I of Austria, as well as two daughters who became queens
Bavaria: King Maximilian II was the father of Kings Ludwig II and Otto
Saxony: King Johann was the father of Kings Albrecht and Georg
Hanover: none that I'm aware of
Prussia: King Friedrich III was the father of Kaiser Wilhelm II of Germany and Queen Sophie of the Hellenes
Württemberg: King Wilhelm I was the father of King Karl of Württemberg and Queen Sophie of the Netherlands
Can anybody fill me in on the smaller German houses?