I like it (though the image of a tug-of-war scene between the brothers with the Youkai in the middle is stuck in my head now). Since they are associated with the gods, would some of the major/more popular Youkai have temples or shrines? Could that even be a reason why the jackal Youkai wants to help out a son of the pharaoh - by associated himself with the royalty he increases his own status within the Youkai world. Or is the jackal actually acting as a messenger like you said - following the orders of one of the gods who favors the youngest son.