While Eden can be mean and has seniority, so to speak, he's still very much Cy's sub and that shows in the dynamic. He's an extension of Cy and an accessory to him; what he does is what he's allowed to do. He likes hurting Isabelle and has a particular thing for choking her, but Cy keeps him in line and he's still denied certain privileges like orgasms (when Cy says so) and getting to fuck Isabelle anally. From time to time she's also allowed to put on a strapon and peg him. Since they're both Cy's submissives, their dynamic is fluid in that how exactly it works depends on what will get Cy off on a given day.