After Sarah died, Abraham remarried a gal named Keturah. She must have been a relatively young woman because she bore him 6 sons (Isaac's little half-brothers), 7 grandsons (at least) and 3 great-grand-sons.
Additionally, Abraham added some concubines during this period of his life. With these women he bore even more sons. (It seems that there was a somewhat pragmatic view of procreation in the culture during that era in history).
Now, Abraham died at 175 and was buried where Sarah had been buried. At his funeral Isaac and Ishmael stood as brothers... shoulder to shoulder... at the ages of 75 and 88. (Evidently Abraham reconnected with Ishmael after the death of Sarah).
Before Abraham died, he sent his many sons away toward the east and gave everything he had to his favored and promised son, Isaac (and by extension to one of his two teenage grandsons, Jacob or Esau). Additionally, God caused Isaac to prosper after the death of his father. Of course, as God had promised, He blessed Ishmael too. Ishmael had 12 sons who became princes of 12 different castles, towns and eventually... nations!
In Isaac's case, God had given him sons when he was 60 years old. Isaac had waited 20 years before he prayed for God to open his wife's womb. God answered by giving him twins! - Jacob (Israel) and Esau (Edom)... 15 years before the death of Abraham.
The most famous interchange between these two bothers occurred when Esau came home hungry one evening. Jacob "stole" (he would have said "bargained for") the "birthright" which his older twin disdained. Well, technically he "bought” it with a bowl of soup.
Finally, the chapter closes with these words, "Thus Esau despised his birthright." Of course it could have ended with other words, like, "Thus Ishmael despised Isaac; Isaac despised all of his brothers, Jacob despised Esau, and Esau despised Jacob...
No wonder Solomon wrote, "Proverbs 27:10, "Neither go into your brother's house in the day of your calamity." Some of these sibling rivalries leave us with an awfully bitter taste in our mouths. Aren't you glad we have a friend who will stick closer to us than a brother will? (Proverbs 18:19 & 18:24)