Oh, what if one of the friends of the Youkai ends up betraying them later? If they had been working together under the radar and they eventually get exposed then he might be forced to work against the jackal Youkai for his own sake. 
And with all this 'help' , I'm sure the question will eventually come up of whether the Youkai are actually helping the youngest son or just manipulating him for their own gain. What is he really worth to them, other then his title? If the son feels later on that the jackal is using him too much, he might try to break their deal - if he's separated from the jackal this would leave him vulnerable to the other Youkai that are working under the god and against him. Thoughts?