3rd Lane space?
 

Can the 2 offensive players A1 and A2 that are allowed on the lane and may occupy the 2nd lane space, during a free throw, occupy the 3rd lane space if the defense only has 2 players on the lane?
NFHS rules.

Limitations are in 8-1-4. If it's not listed as a limitation, then it's legal. See the case book, too.

This Looks Like A Job For The Mythbusters ...
 

On free throws, there is a maximum of two offensive players and four defensive players in the six marked lane spaces. The defense must be in the first marked lane spaces, above the neutral zone marks, on all free throws. The offense must not occupy the first marked lane spaces, above the neutral zone marks. The shooter and all the players in the designated lane spaces must wait until the ball hits rim or backboard before entering the lane. Players, other than the shooter, and the players in the designated lane spaces, are to remain behind the free throw line extended and behind the three point arc, and may not penetrate the free throw line extended and the three point arc until the ball hits rim or backboard. During a free throw, no opponent, including bench personnel, may disconcert the free thrower. For free throws when there are no rebounders in the marked lane spaces, i.e. technical fouls, the nine nonshooters shall remain behind the free throw line extended and behind the three point arc.

This is probably the most misunderstood rule regarding free throws. 99.9% of players and coaches think the players must stand in backcourt during these free throws. I've known some refs who think so, also. In fact, I've had coaches yell numerous times when opposing players are in their proper place in frontcourt that they have to be in backcourt. Of course, I only let each one yell once. ;)

I don't tell players that they have to be in the backcourt, but if they all want to congregate there, I won't stop them.

I've had the coach in the front court ask me before; because he wanted to talk to his players during the FTs.
I've also had officials move the players to the BC while I administered the FTs.

Short answer, yes they may. The only two spaces which are required to be occupied and by a specific team are the first two nearest the basket, which must be filled by the defense, unless no player's are allowed along the lane for the attempt per rule.

The other four spaces are open to whomever wants them subject to the maximum four and two restrictions for the offense and defense.

You may find this info in the references provided by Bob Jenkins.