folks vs son-in-law

folks

noun
  • The members of one's immediate family, especially one's parents 

  • People in general; everybody or anybody. 

  • The police. 

  • Late 19th and early 20th century migrants to California from Iowa and other parts of the Midwestern United States. 

son-in-law

noun
  • The husband of one's child. 

How often have the words folks and son-in-law occurred in a corpus of books? (source: Google Ngram Viewer )