I have always wanted to know more of Spain’s perspective through Papal negotiations for divorce. They did very little to help Catherine and Mary afterall. Are their any good resources on this side of the equation?.
I would recommend Giles Tremlett's biography of Catherine of Aragon because he used the Spanish archives. For example, he gives details of the Zaragoza tribunal into Henry VIII’s request for an annulment, as well as the Blackfriars court. See http://reviews.theanneboleynfiles.com/catherine-of-aragon-henrys-spanish-queen-by-giles-tremlett/532
Catherine Fletcher's book, "The Divorce of Henry VIII", looks at what was happening in Rome, with the ambassadors, during the negotiations for the annulment, so you may find that interesting too. It doesn't give a Spanish perspective, but it gives details of what the ambassadors were all doing. See http://reviews.theanneboleynfiles.com/the-divorce-of-henry-viii-by-catherine-fletcher/890