Indeed, the whole Dutch royal family remained at home for the celebration of the King's Day.
Due to Queen Maxima's Argentinian origins, it is a bit strange and disappointing that the royal couple (or at least Queen Maxima) could not manage to attend. If King Charles and Queen Camilla of the United Kingdom went as far as postponing their wedding in April 2005 because of the funeral of Pope John Paul II, the Dutch royal couple could probably have postponed the King's Day festivities, couldn't they? Besides, I thought the King's Day was on April 27th, date of King Willem-Alexander's birthday, and not on April 26th...

Anyway, if the Royal couple was bound to remain in the Netherlands for the King's Day, the Dutch government could have at least sent for the Pope's funeral another member of the Royal family, such as Crown Princess Catharina-Amalia, Prince Constantijn, Princess Beatrix or Princess Margriet. Their presence for the King's Day might not have been an absolute necessity, while their absence would have been perfectly understood in those circumstances...

Regarding the jewels, Grand-Duchess Maria-Teresa of Luxembourg wore pearl drop earrings, but indeed, that's all - no brooch, and no necklace:




Mathilde, Queen of the Belgians, wore her pearl choker - which is not her "funeral necklace", as dubbed by Maria-Olivia, but a choker she has regularly worn on various types of occasions, both funerary or more festive, from the beginning of her marriage. She added diamond earstud earrings:



Queen Letizia of Spain wore one of the pearl drop brooches of the Spanish royal collection - I think this one dates back to Queen Victoria-Eugenia and that the round pearl at the top is a bit greyish. Also a pair of pearl drop earrings:



I am not sure if Crown Princess Mette-Marrit of Norway wore jewels. Yet, on the following picture, I thing we can spot the bottom of a pearl drop brooch, hidden behind her hair:



Queen Mary of Denmark wore what seems to be a diamond brooch, but I could not manage to find clear pictures: