A mandatory meeting announcement was sent by Special Messenger to each Demon Prince who was escorted to the Royal Private Chambers.  The Underworld Demon King of Mortal Sins was not eagerly waiting for his so called sons to arrive while his wife, the Queen is sitting by with a table of ornate boxes.
She was patiently sitting there with her hands on her lap. She was way too patient for the Demon King now days. Which was ironically one of her prime qualities that he liked in her when they were first married.
When all of the Demon Princes were finally gathered together, he made his simple ultimatum announcement.
“Listen up, Demon Princes. Number Two Point. I have received your monthly expense accounting. Every one of you have over spent your account by more than double and that does not include the damages that you have cause, the fines the you have incurred or the wrath of Hades himself! Which brings us to this meeting.
I have received a larger number of complaints against you this month from Hades himself. You have made yourselves a total nuisance of yourselves and have put me on probation. That is totally unacceptable! 
Since none of you will take me seriously about your way of life, I must enforce a stronger hold on you. This means that you will suffer greatly! This is what shall happen today.
One. All of your powers have been revoked. You have misused them and will not get them back until you have proved yourself responsible enough to handle yourself.
Two. You will have a very restricted amount of money. None from me or your mother. No charge accounts either.
Three. You will have to go to school on the Surface. 
Four. You will pass the classes that are given to you by your Advisor.
Five. You will date and marry one of the female Humans that your Advisor has chosen.
Six. You will be given a Mortal Sin to rule over when you get back. Other words, you will be a Practicing King in Training. Your Advisor will oversee what is done in your kingdom. 
I hope that all of you understand me because if you don’t, you will remain on the Surface as a human. I have this approved by Hades, himself after a very long prolonged discussion in his chambers.”  The Underworld Demon King of Mortal Sins looked from one Prince to another.