Kommentar zu Bereschit 28:5

אם יעקב ועשו MOTHER OF JACOB AND ESAU — I do not know what the addition of these words is intended to tell us.

THE BROTHER OF REBEKAH, JACOB’s AND ESAU’s MOTHER. Because it stated²⁶³It is obvious that Ramban has in mind the words of Rashi, whose comment upon the expression, Jacob’s and Esau’s mother, was, “I do not know what this intends to tell us.” Ramban then proceeds to offer an explanation. that Isaac commanded Jacob to get a wife from the daughters of Laban, his mother’s brother, Scripture mentions that he was also the brother of Esau’s mother. It would have been proper for Isaac to have commanded Esau likewise, but since he knew that the blessing of Abraham would apply only to Jacob and his seed, he did so only to Jacob. Now Scripture further mentions that Esau heard that his father had commanded Jacob not to take a wife from among the daughters of Canaan²⁶⁴Verse 1 here. and that he should go to his mother’s brother Laban. He [Esau] heeded his father’s will that one not take a wife from among the daughters of Canaan, but he did not act properly and take a wife from the daughters of Laban, despite his [Laban’s] being his mother’s brother. Scripture further mentions that he took her²⁶⁵Mahalath, the daughter of Ishmael. (Verse 9 here.) besides his former wives, and he did not divorce the evil wives since he followed his heart’s desire more than he followed the will of his father.
Vayeitzei

וישלח יצחק, Isaac sent away, etc. Why is Laban described as Rebeccah's brother, something we have known for a long time? Why is Rebeccah described here once more as both Jacob's and Esau's mother?