Premise ---
Queen Elizabeth has died. She did not make James her heir through her will. Who among the living heirs could succeed her to the English throne? Would there be another War of the Roses? Would James take his Scottish army south and take his aunt's throne?
Seymour was unacceptable as the wedding of his parents was not authorized and so considered invalid... The heiress of for Henry VIII’s will is https://en.m.wikipedia.org/wiki/Anne_Stanley,_Countess_of_CastlehavenNitpick: Elizabeth and James were cousins, not aunt and nephew.
More directly, going by Henry VIII's will, the throne should have gone to Edward Seymour, as the senior heir to Mary Tudor. In practice, parliament wanted James, so parliament got James. Someone who knows more than an outline of the period would be able to go into far more detail.
Seymour was unacceptable as the wedding of his parents was not authorized and so considered invalid... The heiress of for Henry VIII’s will is https://en.m.wikipedia.org/wiki/Anne_Stanley,_Countess_of_Castlehaven
So Seymour having an actual marriage could be a possible PoD.Seymour was unacceptable as the wedding of his parents was not authorized and so considered invalid.