what is harper lee trying to tell us about the familys in To kill a Mocking bird ?

This really depends on the family that you mean. Certainly social and economic status has something to do with it. I think that the Finch family is certainly not "traditional" in the context of the American south in that era. There is no mother and a black woman, Calpurnia, takes that role on. The Finch family is functional in so many ways that other families are not. Dill feels neglected and estranged from his mother and step-father. Bob Ewell's family is self-destructive and ultimately doomed. Atticus’s family, although not traditional, is progressive, loving and filled with integrity.