@NoSoup Think of it as them playing in theater, only long term and no one else knows it's an act. It's a bit secretive so that adds to the appeal, and it allows some of them to play out their lives in ways they usually wouldn't. However, because it's all an act and they have the Prime Minister, someone who can break their fall if things truly go south, watching over them then there's no genuine fear that anyone will get hurt. It's all just for fun while also for the sake of the long term happiness of the targets(even if the targets suffer a little in the short term, such as Julia's feelings of inferiority towards Meliarose).
With that said, I'm positive none of them wish harm upon either the prince or Julia and thus they wouldn't dare resort to any seriously harmful acts(such as the "villainess" pushing Julia down the stairs), so ideally this plan shouldn't go south unless a third party gets it in their head to do truly horrible things for Meliarose's(or Julia's) sake without discussing it with any of the "actors(students)" or the "playwright(Prime Minister)." Last thing we need is some idiot thinking it's OK to hurt Julia because she's a nuisance for Meliarose or thinks to get revenge on Meliarose for Julia even if Julia wouldn't want that.