Dear princessofEurope, so sorry because I fear that I'm quiet unable to answer to your questions.
1. For the magnific and delicat diamonds earrings, I'm sure they are ancient and the Queen wore them since a long while - for the great and impressive gala given for the coronation of the shah of Iran, Don Juan Carlos and Doña Sofia were not Kings of Spain but only princes of Spain-
2. I don't know their story, i.e. at whom belong before to be wore by Sofia
3. For the diamonds necklace wore by the Princess of Asturias for the Prado Gala, It's semm tome that the Queen wore it too but in looking for in my archives I didn't find any topic pic of this necklace wore by the Doña Sofia as Princess of Spain or Queen. But, as this collar look, for me, like the same style of the earrings of diamonds, I thing it's a set, a very beautiful set even if it's not the most spetacular set of diamonds of the Spain Royal Familly.
4. At my knoledge, up to know and except for the pre wedding gala dinner, I don't remember to have see the princess of Asturias to wear thhis fathers's in law's gift. But i can be wrong!
______________________________________
For your general remark about the jewels wore by the Princess of Asturias, it's true that since a lot of times, Letizia is begining to wore more important jewelry, modern ones obviously by for her like earrings and bracelet for the birthday of W A of Orange; ancient ones as the rubies set - earrings, neklace, brooche, bracelet- wore for the gala dinner of the slovenian president that we know were belong to th Countess of Barcelone and that the Queen Sofia had worn a little - I found a pic withe the earring and a different necklace-; and to end the ancient set withe the magnific earrings , worn byet by the Quenn very often, and the very refined necklace.
that it's for the most important part of her jewelry. But we can observe too that her earrings diamonds "cassettes" is improving too because she is begining to have a beautifull collection of pairs of diamonds earrings in a style as Cartier or Bulgari is doing now for young woman which fit very well to the princess of Asturais.