Of course in folk stories all these impossible tasks normally get carried out, with the help of various creatures whom our hero has befriended in earlier parts of the story. (With the underlying message being that it's best policy always to do anyone you meet good turns, because you never know, you might need a good turn from them some day.)

But I don't think that would apply in this story. After all, this time it's not the girl or her parents who are laying down those impossible conditions to be met.