I love their expressions... Is this an official manga? What's the title? http://www.manga...

Not sure but the art style looks similar some Clamp manga.

I think its this?.... : http://www.mangago.me/read-manga/x/

Yup that's x1999 by clamp

yes but it's a straight (but with BL hints) manga lol. the clamp girls just love to fool around with their every titles. the little one is inlove with the bigger guy's younger sister.
they do have an actual BL manga tho.

thanks guys!