Sorry, not my type of story. At the current length it is only good for it's takeaway lesson and I honestly have nothing to take away from it.
If you would make it less a fairytale and more a story, you could elaborate on:
• How could they find immortality?
• How are the two father-son groups linked?
• Was the King really immortal and what are the rules of that?
• How does the world look like? Currently the story is pretty lifeless and adding more fluff and extra details could help. Make the characters actual people with their own personality instead of them being chess pieces for the story.
Hope this helps 😊
Thank you very much, @reggaemuffin! This was my first fiction writing. But I understand that I forgot those important points you've mentioned.
Thank you so much for taking the time to guide me! :) I very much appreciate it. And I will wrote another fiction keeping all those points in my mind. ☺