Lane spaces?

[fan]

I know the lane spaces adjacent to the end line shall be occupied by an opponent of the free thrower on a personal foul. However, If teammates of the free thrower choose not to take the next available lane spaces can the other team occupy them or will they remain vacant?
I am also trying to figure out the total area of a marked lane space. How far back does the lane space go? I am a little confused in the rule book (NF) where is says that a player occupying a marked lane space may not have either foot beyond the vertical pane of any edge of the space designated by the neutral zone. I am not sure what is the neutral zone?

Thanks