Rebo Bresen was by no means a fool, in fact, this insightful Crown Prince was smarter than many. He possessed ambition and aspirations. Although somewhat naive to a degree, he was still capable of making harsh, ruthless decisions when necessary, such as resolving to kill his own younger brother.
And the people he brought were carefully selected...
Five personal Death Soldiers, five dark mercenaries, three professional assassins, and two Purple Thorn Shadow Guards, among whom eleven were high-level professionals. Of these, the three assassins and one of the Shadow Guards even held epic professional titles, so they should have been more than capable of handling any tricky situations.