A place to organize the various groups of characters in Life is a Highway.
The Koizumi family is a wealthy family that consists of a mother, a father, and their first year college son.
The Himura family is a small middle class family consisting of a mother, father, and their teenage daughter. The mother is currently pregnant with her second child.
The Minami family is a large higher middle class family. The family consists of a mother, father, a middle schooler boy, two high schoolers: a boy and a girl, and a daughter that recently graduated from Tokyo University.
The Wantanabe family is a middle class family with a single mother and her twin middle school daughters. The parents divorced some years back and the father doesn't keep in contact often.