Your blurb really drew me in. I wish that there was a bit more description in the blurb. I like your concept. I liked your writing style. Your grammar needs a bit more work but that is ok. Also, I think that some of your paragraphs were a bit long.
Read the story now
Your prologue was very interesting at first. The more I read from the prologue, the more repetitive it became. I like that it is from someone else's point of view, but is kind of boring near the end. A lot of unnecessary commentaries.
It is all happening too fast. You should describe William's surroundings. Explain why William doesn't want to be in the quest. Where is all of this happening? How did people find out about the quest? You should explain a bit more about the quest. It is confusing how everything happens so fast. The pace should be a bit slower. How does the king know about the kids? What are the ruled for the quest? Maybe your first chapter should be about the king. Maybe he is thinking of what to do when one of his servants helps give him an idea. Something like that. Maybe the king likes that idea and lets everyone know by having an announcement somewhere...
Your plot is good but your pace needs improvement.
Your story is really good but for the prologue, I think you could start the next chapter for 6 months later...
and you could start chapter 2 for 96 months later...
Instead of writing x months later, I think you can just write it in years.
Overall good job.