End of Half w/ fouls

[MTUMP]

The key element here is that Team B is NOT in final possession here, but Team A is (via the touchback). Thus 10-2-2 is not in effect (clean hands) due to Team A fouling before the final change of possession. Thus enforce 10-2-1b. Replay the down....untimed, of course.
RULE 10-2
ART. 1 . . . It is a double foul if both teams commit fouls, other than unsportsmanlike or nonplayer, during the same live-ball period in which:

a. There is no change of team possession, unless all fouls committed by R are post-scrimmage kick fouls, or

b. There is a change of team possession, and the team in possession at the end of the down fouls prior to final change of possession unless all fouls committed by R are post-scrimmage kick fouls, or