Upon first glance, it appears that we're sacrificing people we've already killed, Nero's wife, Jessica's blackmailer, The cop's bribe-y, and the Boxer's opponent. Or at least thats what I figured happened.
Upon seeing actual gameplay however, it appears we're actually sacrificing other people. Try it out, you use nero's alter and nero's object (Golden inkwell pen), but you don't sacrifice Nero's wife.
I believe rather, you're sacrificing who enabled you to kill.
The ref. was bribed into looking the other way, and he's who's sacrificed by the boxer in his ritual. This is the strongest evidence of this as the stripes in the mans shirt depicts that he is a ref.
Nero's Lawyer gave nero the information about his life insurance policy.
I can't be sure, but the man sacrificed by Jessica is not her blackmailer, as he is lacking glasses and weight, instead I believe this is actually her boss, the show manager, whom would fire her if he ever found out about those pictures.
The cop, again, I can't be sure of, but if he's already killed the bribe-y, then perhaps the man being killed is the mayor who was cracking down on police corruption?
Now, why would we sacrifice these people... It doesn't make much sense... These people are the reason will killed the other 4 victims. The whole point of killing them was to get them off their back....