So there are still imps on the floor? Somehow the candle got set as being lit prematurely, so redoing it does not trigger the poison, and the imps are still waiting for the signal saying the candle has been lit for the first time.
I could get the inventory files so you could replace the key that you can not get from the imp skeleton (ie
Inventory files), but it would probably be easier for you to just use the technique described in the topic
armory trick in act 1 to get a summoning doll into the locked room, and loot the chests that way.
I don't recall anything special in those chests, so if you skipped them to continue with the game, you probably didn't miss much.