Michael D. Coogan, The Old Testament: A Historical and Literary Introduction to the Hebrew Scriptures, third edition (OUP, 2014), 89.
The further removed biblical writers are from the events they describe, the less secure are modern scholars’ attempts to determine whether these events actually happened. With regard to Abraham and Sarah, Isaac and Rebekah, and Jacob and his family, we are for the most part in the realm of legend, and it is extremely difficult to determine if any of the traditions concerning them in Genesis 12-50 have a historical basis. An analogy from British history is King Arthur, who may have been an actual historical figure, but the repeatedly retold legends about him are our only sources, making historical judgments difficult.
The quest for historicity is complicated by several factors. First, biblical chronology for this period is unreliable; note especially the long life spans attributed to the ancestors. Second, because so many stages of composition and editing have shaped the narratives, they often contain anachronistic details, since each generation of storytellers, writers, and editors added elements from their own times. Third, because of the use of different sources in the final form of the narrative, many inconsistencies are found.