What's your ruling?

[kdf5]

10-2-2 . . . If each team fouls during a down in which there is a change of team
possession and the play does not have a post-scrimmage kick foul, the team last
gaining possession may retain the ball, provided:
a. the foul by the team last gaining possession is not prior to the final change
of possession, and
b. the team last gaining possession declines the penalty for its opponent’s
foul(s), other than a nonplayer or unsportsmanlike foul. In this case, the team that was not last in possession has no penalty options until the team last in possession has made its penalty decision on the fouls prior to the change of possession. After that decision by the team last in possession, the team not last in possession may decline or accept the foul by the team last in possession or choose which foul to have enforced in the case that the team last in possession committed more than one foul following the change.

B gets to decline A's penalty then A gets to decline B's penalty, game over.