A and B.
Page 36 in the rulebook:
3. If these surviving Monsters are able to reach the Space with the current Hero, the Sins Player makes his Fight roll according to the Monsters currently in the Hero’s Space (including any that may have been there already). The effects of this roll are resolved against the Hero’s initial roll.
So you'd still have 2 hits left over to use in the Sin's roll against you, but the Sin would still be able to roll 2 more dice to include the Acolyte.
This is not entirely correct. The key is that the Hero applies his roll results in Step 1. He deals 2 damage to the Acolyte to kill it and the other two are dealt to the Avatar, however unsuccessfully. Then steps 2 and 3 happen and the Avatar will retaliate with the Acolyte who was in the Hero's space. You cannot "save" the two dice to apply to the Acolyte in your space. The Hero's attack is finished and only his defensive dice matter at step 3.