Akarui Kazoku Keikaku (YOSHIKAWA Arata)

From here:
A cute story about Honoka and the guys she has to live with (a pair of twins in kindergarten, a junior high student, a high school student, a college student) as well as the other guys she meets in school. Honoka is generally a sweet, naive girl which draws an assortment of guys who instinctively want to protect her and maybe become her boyfriend... ^^;