Crossroad Vol 2 by Shioko Mizuki. A Shojo manga rated Older Teen, published in English by Go! Comi in 2005.

After her grandmother dies, fifteen-year-old Kajitsu Toda moves in with her stepbrothers Taro and Natsu, whom she hasn't seen in seven years. When their irresponsible mother drops off six-year-old Satsuki and vanishes again, the four siblings have to build a household, and a family, of their own. A heartfelt shojo drama about found family and complicated feelings.