Yess I guess
I genuinely don't know but it seems like it could be but, what I see is that he is just the spoiled and rich younger brother who got the only noona/ family member takin away from him. So now he is throwing a temper tantrum.
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.
Umm I'm kinda confused does yuri has a crush on her noona???