it actually should be simple. Been toying with something which is similar in practice. Once a condition is met, all references are disabled. I assume killing Omerta is part of a quest, or has some script already associated with it? If so, tag one prosttute as a persistent reference, and enable it as a parent of all other prosttutes. Then go into that script and run prosttute.disable (where prosttute is whatever reference id you gave him/her). Then voila they are all gone.
At most I am guessing around 40 npcs would have to be changed consisting of two clicks apiece, or one if you highlight them and do it in a single pass. Then just add in that single disable. http://geck.gamesas.com/index.php/Reference#Activate_Parents is a pretty good starting point. Used it myself to learn the commands.
At least thats how I would approach it. But such a mod doesnt really interest me