Who had the most to gain by the death of Edward's sons? Who had the means to get rid of them? The majority of the people alive at the time believed that he murdered his nephews. He was not a popular King. I've never heard of Von Poppelau's claim in any of the books I've read. The boys were never seen again outside the Tower of London. There were pretenders but the truth of their backgrounds were discovered. The Royal Family will not allow DNA testing of the bones that were found beneath a Tower staircase in 1674. Maybe some day that will be allowed to occur.
Prior to his petitioning his Titulus Regius to Parliament...justifying his right to rule as King, Richard had eliminated many of the individuals who had opposed his claim to the throne, which left many absences in Parliament. Nothing sends the message of "support me or else," more than executing the Lords who refused to support your claim. One of his biggest supporters, the Duke of Buckingham had turned on him. He was hunted down and executed. Richard also confiscated monies, titles and estates from those Lords who had opposed him. He stripped Elizabeth Woodville of all the land given her by Edward IV, and then he rewarded his supporters. Once he got what he wanted from Parliament, he dissolved it. His only Parliament opened at Westminster on 23 January 1484 and sat for less than a month before being dissolved. Once Henry Tudor became King, Richard's Titulus Regius was overturned by Parliament.
There are plenty of theories on both sides regarding what happened to the Princes. I choose to believe, based on evidence presented in many of the books I've read, that he murdered his nephews. He had the motive, and the means. There is no proof that he didn't have them killed. It's been suggested that one of the reasons the Duke of Buckingham turned on Richard III was because of his plans to have the Princes murdered. Of course that's speculation, just like a so-called German diplomat's claims the boys were still alive in 1485. Having worked for 25 years in law enforcement, I'm more prone to believe that Richard of Gloucester was a low-down, murdering scoundrel.
If anyone, besides Edward V, and Richard, Duke of York had claim to the throne, it was Edward Plantagenet, George, the Duke of Clarence's son. George had managed to tick off his brothers by supporting the Earl of Warwick (his father-in-law) in rebelling against Edward IV. He was condemned, and put to death by his brother, the King. A Bill of Attainder against his succession was introduced by Edward IV to Parliament, which Richard, Duke of Gloucester could have petitioned Parliament to be reversed, but he never did. He wanted the crown for himself.
for later
Edward, indeed, married Eleanor Talbot. Robert Stillington was a witness to it. Here is Paul Murray Kendall on the subject: “In the eyes of the Church, the essence of marriage was consent, a mutual interchange of personal vows; therefore, betrothal had the force of a legal tie and the sanction of sacred obligation.” Henry 8 used Anne Boleyn’s supposed betrothal to the Earl of Northumberland to get rid of her. We cannot view betrothal in a modern way. It was legally binding and used to put aside a child king who would have been a disaster given his villainous mother and her villainous and rapacious family.
Nicholas Von Poppolau was a diplomat, not a “so-called” diplomat. His account of staying with Richard 3 several months before Bosworth Field is one of the few real glimpses we have of this maligned king. He reports that the boys were alive. Von Poppolau turns up in every decent history book written about R3. There is now a tantilizing hint put forward by my friend, Stephen Lark, that the children were seen at Gipping Hall in Suffolk. That was the ancestral home of the much-maligned and lied-about Sir James Tyrell. It’s been suggested that this is where they were sent before slipping into the continent. (This is still speculation.)
I’m not going to bandy words and try to prove a negative - even with a law enforcement professional. Believe what you want to believe about the disappearance of those children. But I wouldn’t take the remains in the urns at Westminster Abbey too seriously. From their brief examination we are not even sure if they were male or female or from what era they were from. And one had a serious jaw disease. Neither of the princes was reported to have that. Elizabeth 2 will not allow the urn to be reopened - perhaps Charles will. I think it will be akin to Al Capone’s vault.