Phoenix2000

like i said in a post earlier, if you talk to them again you can still kill them by trying to intimidate them then saying you want to fight. i did it and the rest of the quest was easy

I got it to work just by talking to the guards again. i made the same mistake you did in not killing them earlier, however, you can select an intimidate option if you talk to one and say something along the lines of, "you wanted a fight, lets do it..." you will gain the dark side points and the path will be cleared (the dark side points are canceled out by the light side points you gain from completing the quest)