First you need to be a gang member, and then first you need to corrupt Nichole enough before you do the basement scene where you announce to Bruce and Davide that she's your slut, and there you can tell them both that they're not allowed to touch her, she's yours. You can even tell who Bruce is allowed to fuck, or is he allowed to fuck anybody, maybe you can tell him that the only pussy he's allowed to have is the junkie girl in the subway xD
Once you've done that, then you can do the same with Cassandra

There also a scene in the basement with Alexis, a sex scene, corruption path, all those are corruption paths with each girl
But it's important that you do Nichole first, because if you try to do Cassandra first, Nichole will interrupt it because she doesn't approve it. But if Nichole is your slut first, then she has no choice but to allow Cassandra be your slut too