[Adam]

I don't think this case play works here, as Bob indicated it might not.
1. In the OP, the ball has not been released. In the case play, it has.
2. If the ball had been released for the free throw, there's no question it should count.
3. Since the question is what happens when there's a double foul between B1 and A2 after A1 has started his shooting motion but before it's released, I think the differences from the case play negate its usefulness on this.
4. The case play is using the fact that the only thing that can cause a released try to become dead before it is naturally completed is a player control foul. Since the free throw situation does not involve a differentiation of player control foul from team control foul, it's not relevant.

Unless something specifically states otherwise, I have to think the foul by a teammate causes the ball to become dead unless the try has already been released.