To search the Library's collection of plays, use the Advanced Keyword Search, select 'Subject keywords' from the first drop down menu and type in your topic (families, marriage, parent). Next, type in "Drama collection" in the second search box.
You can also use an index such as the Critical Survey of Drama to look up plays. Use the subject index in the back to find plays that relate to your topic, then look up the title of the play in the Library Catalogue to see if it's available.
Critical Survey of Drama