Here’s the answer:
Abraham had 8 sons.
1) Ishmael- mother is Hagar
2) Isaac - mother is Sarah
3) Zimran - mother is Keturah
4) Jokshan - mother is Keturah
5) Medan - mother is Keturah
6) Midian - mother is Keturah
7) Ishbak - mother is Keturah
8) Shuah- mother is Keturah
Genesis 25:1-2
Then again Abraham took a wife, and her name was Keturah.
And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah.