In-law
A in-law was a relative by marriage, rather than by blood or adoption. The term was still in use in the late 24th century. 

In 1947, Lieutenant General Denning of the United States Army Air Forces derogatorily remarked upon the similarity of Quark's behavior to that of his brother-in-law, who was a car salesman. ()

In 2373, when a Takarian sandal maker was asked by  and Doctor Arridor why his shop was failing, he explained that his mother-in-law was ill and his children were too young to work. ()

While pondering his future as a potential Grand Nagus in 2375, Quark referred to Leeta as his lovely sister-in law. ()

In 2376, Reginald Barclay seemed surprised that Commander Pete Harkins would approve of Barclay dating his sister-in-law Hope. He expressed his doubts about his worthiness as a "catch", citing his history of erratic behavior. ()

List of in-laws 
 Baron , father-in-law of Harcourt Fenton Mudd
 Hope, sister-in-law of Pete Harkins
 Ishka, mother-in-law of Leeta
 Aurelan Kirk, sister-in-law of James T. Kirk
 George and Winona Kirk, parents-in-law of Aurelan Kirk
 Owen Paris, father-in-law of B'Elanna Torres
 Owen Paris, father-in-law of Kes (alternate timeline)
 Tom Paris and Kes, parents-in-law of Harry Kim (alternate timeline)
 Marie Picard, sister-in-law of Jean-Luc Picard
 Quark, brother-in-law of Leeta
 Kyle Riker, father-in-law of Deanna Troi
 Joseph Sisko, father-in-law of Jennifer Sisko and Kasidy Yates
 Judith Sisko, sister-in-law of Jennifer Sisko and Kasidy Yates
 Lwaxana Troi, mother-in-law of William T. Riker

External link 
 
Law
Family