On a face off, do the wing middies have to stay inside the end of the wing area line? The line is ten tards long on either side of the center line. Can a player be fifteen yards off the centerline as long as he is behind the wing line?

no, the players need to be in the wing areas at the time of the whistle. 1.2.5 defines the wing area in part by saying "The areas between these line segments[, the wing area lines,] and the sidelines and confined within the extremites of those line segments shall be designated as wing area."

I take it when it says "confined within the extrmenites" to mean that the wing areas are bound by the fixed length of the wing area lines.