Rainmaker,
Here is the EXACT wording of the interpretation of your play directly from the NFHS website.
http://www.nfhs.org
SITUATION 18: B1 illegally steps into the lane before A1's final free throw hits the rim. A2 then steps into the lane prematurely and then commits basket interference. RULING: The first infraction by the defensive player B1 does not end the free throw and is a "delayed" free-throw violation; the ball is still live. When A2 enters the lane prematurely, the violation is ignored. But when A2 commits basket interference, the ball becomes dead immediately and ends the free throw and no point can be scored. Therefore, the free throw is unsuccessful and A1 would be given a substitute throw. Play is resumed from the free-throw situation. (9-1-9 Pen 2b; 6-7-9; 4-20-3)