Mothers

בראשית מד,יט: הֲיֵשׁ־לָכֶם אָב אוֹ־אָח

The Baal HaTurim writes that Yosef did not ask the brothers about their mother because he already knew that she had died.

Yosef was about 8 years old when his mother, Rochel, died which is mentioned in the Torah. The Torah does not mention when the Yaacov’s other wives died. The Sedar Olam states that Leah died prior to the sale of Yosef around the time that the brothers’ jealously arose against Yosef. Further, another Medrash relates that when Yaacov accompanied Yosef on the first leg of the trip to his brothers, Yosef asked Yaacov why he had buried Leah in the Cave of Machpelah. A question does remain why Yosef did not ask about Bilhah who had raised Yosef after his mother’s passing.