Maria Thins
Maria Thins( c. 1593 – 27 December 1680) was the mother- in- law of Johannes Vermeer and a member of the Gouda Thins family.
Vera Miletić
Vera Miletić (Serbian Cyrillic: Вера Милетић; 8 March 1920 – 7 September 1944) was a Serbian student and soldier.
She was notable for being the mother of Mira Marković, posthumously making her the mother-in-law of Serbian president Slobodan Milošević.
John VI, Duke of Mecklenburg
John VI, Duke of Mecklenburg( 1439 – 1474) was a Duke of Mecklenburg.
Eldon Howard
Eldon Howard was a British screenwriter.
She was the mother- in- law of Edward J. Danziger and wrote a number of the screenplays for films by his company Danziger Productions.
Duchess Gustave Caroline of Mecklenburg-Strelitz
Duchess Gustave Caroline of Mecklenburg- Strelitz( 12 July 1694 – 13 April 1748) was a daughter of Adolphus Frederick II, Duke of Mecklenburg and Princess Maria of Mecklenburg.
Marian Shields Robinson
Marian Lois Robinson( née Shields; born July 29, 1937) is the mother of Michelle Obama, former First Lady of the United States, and Craig Robinson, a basketball executive, and the mother- in- law of former U.S. President Barack Obama.
Duke William of Mecklenburg-Schwerin
Willem of Mecklenburg-Schwerin (Ludwigsburg, 5 March 1827 - Heidelberg, 28 July 1879), was the second son of Hereditary Grand Duke Paul Friedrich of Mecklenburg and his wife Princess Alexandrine of Prussia, daughter of Frederick William III.
Priscilla Pointer
Priscilla Marie Pointer( born May 18, 1924) is an American stage, film and television character actress.
She began her career in the theater, including productions on Broadway.
Later, Pointer moved to Hollywood to act in films and on television.
She is the mother of Amy Irving, therefore making her the former mother- in- law of filmmakers Steven Spielberg and Bruno Barreto and the mother- in- law of documentary filmmaker Kenneth Bowser, Jr.
Princess Alexandrine of Prussia (1842–1906)
Princess Frederica Wilhelmina Louise Elisabeth "Alexandrine" of Prussia (1 February 1842 – 26 March 1906) was a member of the House of Hohenzollern as the daughter of Prince Albert of Prussia and his wife Princess Marianne of the Netherlands.
Cornelia (mother of the Gracchi)
Cornelia( c. 190s – c. 115 BC) was the second daughter of Publius Cornelius Scipio Africanus, the hero of the Second Punic War, and Aemilia Paulla.
She is remembered as a prototypical example of a virtuous Roman woman.
She was the mother of the Gracchi brothers, and the mother- in- law of Scipio Aemilianus.

Question: Who is Duke William Of Mecklenburg-Schwerin's mother-in-law?
Answer: Princess Marianne of the Netherlands