John de la Pole was already married (sometime in the late 70s to Margaret FitzAlan niece of Queen Elizabeth Wydeville) - there were no others really of age to marry Elizabeth of York - Edmund was the same age as Edward V so about five years younger than Elizabeth with William and Richard even younger. Why would Elizabeth escape though - Richard III had arranged a marriage for Cecily of York but kept Elizabeth single - if she escaped Richard's custody then you can guarantee where she ended up she would have been regarded as a useful political tool - say she ships herself off to her half brother Dorset - then the Tudor wedding happens earlier - north of the border then don't rule out a speedy marriage with the future James IV and a Scots invasion.
Henry of course was well aware his acceptance in wider circles was in part down to his marriage to Edward IV's daughter. He of course made damn sure that he was proclaimed by Parliament as "king by right of conquest" not by inheritance - negating the claims of anyone other than himself and his heirs.
Hmm very true.
I've always wondered, had Richard's son Edward survived would he have considered marrying him to Elizabeth, or would that merely undermine his own legitimacy?