
Umm I'm kinda confused does yuri has a crush on her noona???

Yes, though I don't know if she is really his sister 'cos they don't look alike. I think in the sumary it's say she is his cousin. I think it's common in oriental countries to call "brother" or "sister" to cousins, I've seen that in others mangas too.
Whos the last guy at chap. 24 and 25,