if two players are playing the same FW, the opponent of the first who reveals the wizard has to discard all stage resources specific of that wizard. But:

what happens whit cards like an untimely brood or a strident spawn if they are already in play?

are those discarded too?

If none of these cards is in play, can the player who hasn't revealed the wizard play any of them?

or since the opponent has revealed the wizard first you are no longer considered to be that wizard anymore and in consecuence can't play untimely brood/strident spawn?