The Song girl is offering him a pittance even if he solos the boss. It isn't worth it to reveal his true power. Better to just go in alone after they fail.
Public stealing of an awakened class, with no whatsoever consequences? To answer the headmaster's question, 'Yes, the laws are obviously just for decoration'.
Warlock -> acknowledged by "the Fire Demon" -> upgraded to "Holy Lord", including some "Demon Points"? Demons are about the exact counterpart to anything "holy"...
[plus, personal opinion: Not a fan of the "We're family? Great, let's slaughter each other..."-trope]
edit after watching the whole thing anyway: The story itself is good enough despite the poor start. The 'family dispute' is altogether handled poorly though; not a single reputable institution would EVER accept a petty thief with generally questionable character from a poor family background (talking about morals&values there, not money...); it's not exactly great advertising to invite a lowly thug after all, and would realistically stop any decent person from even wanting to enroll there.
"I need to hide my power from my family until im strong enough to defy them. The best way to do that is to accept missions in a high level dungeon someone with mediocre power has no business entering."
So yeah, they broke the law and stole a class. Don't know what the punishment will be but if it's not execution for all parties involved, that's bullshit.
This MC is a pos. He gets payed to go into a dungeon to do work,. But he stays in the back looking at people getting destroyed until they make him do his job.
His Father STOLE His S-Rank Class for His Younger Brother—Then He Awakened 8 DEMON POWERS