[Fifth And Goal]

I meant that both players land on 2 feet simultaneously. A1, thinking that A2 is an opponent, moves 1 foot back while still holding the ball in an effort to rip it away. A1 and A2 maintain joint possession of the ball, and A2 never moves. Travel?

I say no, because A1's set foot and A2's feet are collectively the "pivot foot." So long as A2 never moves either foot, then we play on.