oh OOOOOOH their deaths mirror each other. Tamerlane and Leo are both driven to what looks like suicide chasing hallucinations around an apartment that architecturally represents their psyche (as they destroy it), shortly after leaving/planning to leave their loving partner. (Both of them invite her in, at first. Both of them want her there. But now she's in the mirrors. She's in the walls.)
Vic and Camille are both killed/driven to death by Vic's experiments, their rivalry leading to both their deaths (Camille to prove it doesn't work, Vic to prove it does), immediately after they get left by people they are using in professional/personal ways - Camille hires Toby and Tina to sleep with them, Vic dates Ali to get her to work with her on the heart mesh.
Perry and Frederick both die in the same warehouse, looking at the ceiling, waiting for death to come to them - Perry with a look of ecstasy, Frederick in terror. Both of them are in that warehouse because they've been humiliated by Roderick and are now determined to prove themselves. Both get led here by drugs. Both involve the mutilation of an innocent, Morrie. Both of them see Verna not as another character, but something like her true self. And there's the parallel between all the mercy that Verna offers Perry - the most she offers any of them, other than Lenore - and her glee in explaining to Roderick exactly why he deserves to die like this.
And then you get the final pairing/quartet of deaths - Eliza Usher + William Longfellow vs Madeline and Roderick which is obvious but oh my god. oh my god you guys. Eliza's wall of crucifixes and clinging to Christian faith and the sanctity of pain as a way of hoping for reward after death vs Roderick putting Madeline through the agony of vivisection to 'honour' her + grant her Egyptian immortality. Both William and Roderick eat their young. Fuck.