both main characters are the youngest in the family and loved and doted on by their older brothers
both suffer from an inferiority complex, after comparing themselves to their older brothers (for different reasons though, and in minna ai no seine it develops due to the brothers behaviour)
Both are stories about a middle school kid that's standing in the shadow of their dazzling family members. Both of them have issue's with being not so pretty or talented as their parents or siblings, unable to realise they are the center of their family-universe.
Both are about a highly likeable protagonist who is considered the one plain-looking member of an otherwise gorgeous family, and though Sonnan ja nee yo gradually turns romantic, both are pretty darn funny.
One volume manga series about the cute and often silly experiences of a set of four siblings -- with the main difference being that Clover is about four girls and gives everything a girls love tinge, while Family Complex has both boys and girls and more diverse subject matter. (Natsuru's section would be right at home in the midst of Clover's chapters, though!)