Because I've been able to play The Darkness multiple times, my opponent's deck now has more than 3 candles in it. What happens to each of my The Darkness's when the third candle is drawn? Do all of my The Darkness minions awaken or do they each have their own timer or does each candle function based on each The Darkness minion?
The Candles shuffled into your opponents deck are not tied to a specific The Darkness minion. In other words, if you shuffle more than 3 Candle cards into your opponent's deck, then all of your Darkness minions will "wake up" sooner.
This is can be shown simply enough in a single-player practice match with the Innkeeper, but it can also be shown as the strategy of shuffling multiple Candles was the main point of a deck suggested by Mike Donais, a senior game designer of Hearthstone.
So your deck has great potential!