Well, looking at the pool’s results, I decided to create a reasonable and fair sonko challenge. Thanks for everybody. 
Sonko Challenge #116.
PS id: 2-29-8525800-09
PC id: 1-29-7213984-91 (thanks @StatelessSword)
Xbox id: 3-29-4323348-80, (thanks @Mark_penrose)
Targets
Kill condition is “Any” to all of them.
Hanna Gerhard is the female staff member inside the “little office” just after the club’s entrance.
Hagen Bischoffs is the male bartender in the bar in the relax area.
Alban Jager is the bartender serving in the juice bar, still in the relax area.
Finally, Bianka Krantz is the female technician near the DJ’s booth, close to another technician and a dj. She’s the one operating on a laptop.
About the scrapped contract concept
The initial concept was about a contract in Sapienza, where you have to kill the Red Plumbrer with the Katana and the Green one with the sapphere axe: I was aware that a contract like that, with the Sonko restriction, would be too much tedious, and also too much time consuming just for making backtracking in the map two times in a row carrying unconcenable weapons. I understand it’s more a bad contract than a reasonable and fun one. Maybe I’ll try to create it someday, but otherwise I decided to leave this concept away from the Sonko challenge thread.
As usual, good hunt agents.