Israel Finkelstein & Thomas Römer wrote a pair of interesting articles on the subject of narratives in the Torah/Pentateuch (HeBAI 2014; ZAW 2014).
sci-hub.tw/10.1628/219222…
academia.edu/28570571/I._Fi…
theologie.uzh.ch/dam/jcr:b79ce6…
academia.edu/22081309/Finke…
sci-hub.tw/10.1628/219222…
academia.edu/28570571/I._Fi…
theologie.uzh.ch/dam/jcr:b79ce6…
academia.edu/22081309/Finke…
I'll summarize their reconstruction of how the narratives came together. First of all, there were actually three origin stories: Abraham, Jacob, and the exodus (i.e. Moses).
The exodus story was a charter myth for the northern kingdom in the time of Jeroboam and was strongly associated with the cities of Shechem, Bethel, and Dan (probably the latter two not until the 8th century BC).
The Jacob cycle was another alternative charter myth for the origin of the northern kingdom, originally arising from local legends about certain places. The oldest legends of Jacob arose in the Gilead area, but in the 8th century in the time of Jeroboam II, ...
Jacob became a hero of the central highlands as well and thus became associated with Bethel, Shechem, and other cities (as a consolidation of the Jacob narrative with exodus tradition). Hosea in the 8th century contrasts both origin stories and holds the exodus in high esteem...
...while regarding the Jacob traditions poorly. He also was familiar with both the Jacob-Laban block of tradition as well as the Jacob-Esau block, though in the latter the brother was unnamed.
Abraham appears in later extra-Pentateuchal sources from the 6th century BC (Ezekiel and Deutero-Isaiah). He arose as a local etiological hero in the southern kingdom of Judah, associated first probably with the cultic site of the Oak of Mamre, but...
...also later with other southern sites lying at political borders such as Beersheba, the Dead Sea, and Gerar. Like Jacob, he was remembered as the father of the nation. Finkelstein and Römer believe that the Jacob cycle was imported to Judah after 720 BC...
...when the northern kingdom fell to the Assyrians, and then Judeans composed an Abraham cycle out of their own local hero in the 7th century BC. The Jacob-Esau brotherly conflict was imitated in the Isaac-Ishmael narrative.
Ishmael gives a clear indication of date since the name alludes to the Shumu’il confederation which flourished in the 7th century BC (reflecting a southern expansion of Judah under Assyrian hegemony) but which came to an end by the 6th century.
The Lot narrative pertaining to the origin of the nations of Moab and Ammon were also more pertinent to the 7th century as well. The Judean author subordinated the Jacob stories by placing Abraham first chronologically and also by making Abraham imitate various deeds of Jacob,...
...such as going first to Bethel and Shechem ahead of Jacob. From the allusion in Amos 7, it is possible that Isaac was an independent local ancestor in the south (Beersheba?) who was then integrated with the Abraham cycle as his son.
Then the two cycles, Abraham and Jacob, were glued together by making Isaac the father of Jacob. The reign of Josiah is a logical time for the composition of this combined narrative; note also Moriah as the place of animal sacrifice in Genesis 22...
...which clearly reflects a southern perspective and presuppose the centralization of the cult in Jerusalem under Josiah. (The Joseph novella was also possibly composed around this time in the Saite period in order to link together the Jacob cycle with the exodus narrative).
The next stage of the process was the composition of P, probably in the exilic or the early post-exilic periods. P gives a coherent rewritten story of Abraham and Jacob with some major changes. Abraham is made a Mesopotamian from Ur of the Chaldeans and Haran...
..., the capital of Assyria in the early Neo-Babylonian period, is also his home. This reflects the situation of the Babylonian golah and the wish for them to return to land of Israel. Another innovation of P was Machpelah, which brought all 3 patriarchs into Judah for burial.
The older tradition was likely that Jacob was buried in Shechem; there was indeed a later tradition of this (contradicting P) as found in Acts 7:16 and Jerome (cf. also John 4:5-6 on an example of a local Shechemite Jacob tradition).
The last parts of the Abraham narrative to be redacted in the Torah, according to Finkelstein and Römer were likely Genesis 14 (with the very late Melchizedek insertion) and 15.
