Many books on human families are located in the HQ section. If you want to see further breakdown of this section (for example, section HQ 1058 for books about widows and widowers), look at this document. You might also find the GN 301-674 section helpful, as it contains materials on ethnology and social and cultural anthropology.
If you have any trouble locating the materials you need, we recommend searching in the library catalog or stopping by the front desk to talk to a librarian.