Careful, Peil, There's a glitch in your logic. The problem is, that promise was made to Abraham who had how many kids? Let's see.
Wife 1: Sarah
Isaac: the father of Jacob and Esau - Jacob is Israel
Wife 2: Hagar
Ishmael
Wife 3: Keturah
Midian, Zimran, Jokshan, Medan, Ishbak, Shuah...