Fallen: Synn

When the four princes of Hell (Obsidia to those who live there) overstep their bounds, the king banishes them to Earth for a hundred years--the very place they seem to be so fond of. At first they think it's going to be Heaven, but then the king of Obsidia wouldn't have his reputation without reason, and those reasons happen to be conditions; Castiel, Synn, Myurin and Bastien are not allowed to use their demonic powers for personal gain, affect free-will, reveal themselves in any sense, disrupt Earth in negative light, and they are absolutely not allowed to fall in love. If that isn't enough, breaking any or all of these rules would result in permanent banishment and the loss of their immortality--something a prince of Obsidia (or anyone, for that matter) would rather die than be subjected to.
So it is that the four brothers are thrown into the human world and left to fend for themselves with no money, and no clue, and hope to the Devil they fit in. The problem is, they don't fit in. After all, they're not angels, and devils can't help but break the rules. . .

Castiel ------ Castiel 2
Synn
Myurin
Bastien ------- Bastien 2
Jeriah
Pearl