Can’t say anything to the first part, will need to actually open the book for that. 
77%
It’s the other way around, the あちら側 is where 恵子 is actually at, where she doesn’t have a problem with anything that’s happening, and こちら側 is where the sister can help her with her “problems”. Pretty sure this is, from the sister’s pov.
Didn’t this imagery come up before in the book? Something to look up later. 
I was so blown away when he showed up to her rescue, too! Maybe meeting 恵子 helped him see some things from a different perspective? But yeah, maybe he’s just protecting his habitat… Even so, that kind of goes against his reason for even being there (which was to not have to deal with society’s expectations - which he’s actually confronting as in dealing with now). Nect week can’t come soon enough! 
I was also pretty sad with how her sister handled this situation. Especially since she was introduced as 恵子’s supporter, who even helps her make excuses and fit in better. Maybe the ‘hope’ that 恵子 was “fixed” now prevented her thinking clearly.
That last scene, where her sister and 白羽 are enacting this… I want to call it a play, almost, and she’s just watching as a spectator felt like a pretty alt description of everyone’s status in society. With her sister as the normal part of it, 白羽 sort of not fitting in and getting scolded, and 恵子 as the actual outsider removed from society, where neither part actually knows what to do with each other.
I might be reading too much into that. 



Not トゥアンくん!!! 




I think it’s more about being forceful. I think the closest jisho’s definition is “to be full of vigor”.
