2: Abraham's second son was Isaac (Gen 21:3). Isaac had a second son called Jacob (Gen 25:26). Jacob who was later renamed to Israel had the 12 patriarchs, the twelve Tribes of Israel. The Fourth son was called Judah (Which the Jews of today are descendants of.)

Gen 21:3  And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.
Gen 25:26  And after that came his brother out, and his hand took hold on Esau's heel; and his name was called Jacob: and Isaac was threescore years old when she bare them.