Last play penalty question and enforcement

[bisonlj]

When giving the options to B, I would probably be as thorough as possible:

If you accept A's penalty, we'll have a double foul and replay the down for A
If you decline B's penalty, you'll get the ball at the A25 (assume 10-yard illegal block) IF A accepts your penalty. If they decline your penalty, the game will be over.

You don't let A decide before B decides but you let B know the full impact of their decisions.