The Spanish has a few mistakes:
Alexander - Alejandro
James - Jaime
Jacob - Jacobo
Diego would also do, but would not probably do for a king.
If you want an old style form, Yago would also do (where Santiago comes from)
Nicholas - Nicolás
And may I add Catalan to the list
Alexander - Alexandre
Alphonse - Alfons
Andrew - Andreu
Catherine - Catalina
Charles - Carles
David - David
Edward - Eduard
Elisabeth - Isabel
Ferdinand - Ferràn
Francis - Francesc
Frederick - Frederic
George - Jordi
Henry - Enric
James - Jaume
Joan - Joana
John - Joan
Joseph - Josep
Lewis - Lluís
Margaret - Margarida
Mark - Marc
Mary - María
Matthew - Mateu
Michael - Miquel
Nicholas - Nicolau
Paul - Pau
Peter - Pere
Philip - Felip
Richard - Ricard
Robert - Robert
Stephen - Esteve
Theodore - Teodor
Thomas - Tomàs
William - Guillem
Victor - Víctor
Notes on Catalan names not in your list which are quite common:
Joachim - Joaquim
Earnest - Ernest
Vincent - Vicent
Montserrat - Montserrat (feminine)
Meritxell - Meritxell (feminine) is pretty much the national common name in Andorra (famous Virgin apparition)
Special mention for Pau which is gender neutral as it means both Paul(masculine) and Peace(feminine)
In Spanish they would be Joaquín, Ernesto, Vicente
Pau in Spanish would be Paz if feminine, and is also relatively common.
Relatively common in peninsular Spanish is Concepción (feminine), which is not used in South America. The familiar form for it is Conchita, which can mean "little shell" and in South American Spanish "a certain part of the female anatomy".
Oddly enough, while Catalan names are very uncommon outside of Catalonia, some Basque names are relatively and consistently popular in Spanish (and Catalan).
Aitana (Gloria), Ainhoa (virgin), Ainara (swallow), Begoña(under foot) for girls
Aitor (good father), Gorka (farmer - could be George?) for boys
Aitana has apparently found its way into Portuguese as well.
Obligatory humorous aside.
For those that know a bit of Spanish and were not aware of it, the most original names in the whole known Universe have to be the people of Santo Domingo.
Where else can you find people who have as first name:
Winston Churchil (and then the surnames), Elton Jhon (yes, Jhon), Bruce Lee,
Peligroso (dangerous), Adicto (addicted), Anal (yes, that), Hirohito, Chicle Faustino (Chewing Gum Faustino), Mazda Altagracia, Coca (Coke), Rambo, Gandalf, Alien (surnames Sesale -pretty much ComesOut- and Yedi, yes, Jedi), Joe Dimagio Fernandez, Baby Ruth Tejeda...
... the moment you find a guy named Calendario (calendar) and then another called Thermo, followed by Hervido (boiled), Celsius and Fahrenheit...
...I can only conclude we're too freaking boring. These people have no fear of ridicule and I salute them.