This is essentially Case Play 3-4-7 C.
Since it's live ball by B followed by dead ball by A, enforce B's foul and give A the option to delay the clock, then enforce A's foul and give B the option to delay.
By rule, what sczeebra said. By pragmatism, what NVFOA_Ump said - at the very least, give team B a very leading question "The clock will start on the snap, right?"