So yeah, I don't know if I ever explicitly said this, but Gemini's family are all assassins (except Alexeev). So yeah, here's where I talk about specifics, so you can stop reading now if you so desire/need to. There's nothing particularly graphic written below, so I didn't mark it as mature, but here's my personal warning nonetheless.
They aren't freelancers nor can you buy their services with enough money. They do their work as part of a cult. There isn't anything particularly odd about their cult sans the fact that they do believe that there are people who /should/ be removed from society by any means necessary. -cont-

Now, this group also believes that threats and only threats to society should be removed. This means that they put a significant amount of energy in trying to detain wrongdoers the legal way to minimize disruptions to non-member, law-abiding citizens.
Of course, when the established law is too incompetent to get the job done, they'll just murder their target. Boss, Gemini, and Silent belong to the section of the organization that deals with "extermination" as they call it.
While there are many varieties of jobs that deal with extermination, but you can generally say that there are those who plan the murder, those who actually commit murder, and those who clean up the aftermath.
Boss predominately commits murder primarily due to his strength and physical skill. Gemini usually commits murder, but occasionally plays "clean-up" since he has the training. Obviously, Silent is capable and commits murder due her immense strength, but she often plans other murders due to her intelligence. -done-