Well I think the cells do play it's part, but it's prolly also because Kanou improved his experimenting even further. Which reminds me that I really wonder why a former CCG professor would side with Aogiri Tree. He seems to have a screw or two loose (like quite a few people in TG

) but he's not exactly what I would insane, so he prolly has a sowewhat understandable reason once some mysteries get solved.
Hmm can't say they seem particularly close tbh. The whole mother and father thing is just his charade to pretend happy family. Haineki is well aware that something is completely off, but he's too afraid of facing the truth, prolly because he doesn't want to lose the little peace he gained (again). As for Arima, I never felt like the guy was showing strong emotions to anyone. He's still one big mystery to me, so I'm unsure how he actually feels about others. I mean Arima and Haineki surely have a connection, but nothing implies that it's anything beyond curiosity and duty (from Arima's side) or gratitude and pretending to have a happy life (from Haineki's side). Honestly, I think once Haineki finally remembers everything the bond will prolly break rather easily.
Well others might come somewhat close to them, Uta for example seems to be pretty damn powerful too. The Clown's are a rather big wildcard, and I feel like they might just be the final enemy in the end. Once either side falls I imagine the clowns will either kill Arima or Eto (as I imagine once they clash for real that's the deciding battle) and ruin everything.
Then there's Rize too, I really wonder what happened to her/how she changed during the timeskip. So many people to think about and so hard to predict anything, that's why I like TG XD