I might be crazy, but this seems a variant of the Labyrinth puzzle. (David Bowie in tights, that's all one needs in life). Also, see: http://www.xkcd.com/246/
I believe that a different variant of it was stated before by someone whose name I've forgotten. However, I think that, as a variant of this puzzle, the answer will be a variant of the answer to this puzzle.
The trick is to find an question where each answer yeilds the same result. For example, in the labyrinth puzzle, Sara asks the guard, "Which door would the other guard tell me to use," leaving her able to see, then, that whichever door the guard she asked said would be the road to certain doom. (I find this easiest explained by saying that, if she asks the liar, he says that the one who would tell the truth would tell her to go through the door that leads to certain doom, because he himself lies. If she asks the one that tells the truth, he says that the one that lies would tell her to go through the door that leads to certain doom because he - the door that lies - lies. The third one just stabs people who ask tricky questions.)
Regardless, I feel like the answer to this is along that vein.
As a charming and handsome, gallant, knightly prince, shooting or stabbing each princess for any length of time is completely out of the question.
I don't feel like there would have been a puzzle posted without a possible solution. Perhaps the original poster is just mean/doesn't know the answer himself, but I doubt it.
So, I think that if you ask any sister,
I think I'm close, but not there yet.