aunt-in-law vs stepsister

aunt-in-law

noun
  • The wife of one's uncle or aunt (parent's sibling). 

  • The aunt of one's husband. 

  • The aunt of one's wife. 

stepsister

noun
  • The stepdaughter of one's parent which is not one's half-sister. 

  • The daughter of one's stepparent who is not the daughter of either of one's parents. 

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