Discuss Sue's answer to: Who were the wives of Abraham, the patriarch?

Sarah was the first wife of Abraham. But,who would be Abraham’s heir?
Despite promises of a seed, Sarah remained barren.

Genesis 16:1-3
King James Version (KJV)

16 Now Sarai Abram's wife bare him no children: and she had an handmaid, an Egyptian, whose name was Hagar.
2 And Sarai said unto Abram, Behold now, the Lord hath restrained me from bearing: I pray thee, go in unto my maid; it may be that I may obtain children by her. And Abram hearkened to the voice of Sarai.
3 And Sarai Abram's wife took Hagar her maid the Egyptian, after Abram had dwelt ten years in the land of Canaan, and gave her to her husband Abram to be his wife.

So, Hagar was wife # 2. She bore a son named Ishmael.

Later, Sarah , did give birth to a son, whose name was Isaac.

Gen.21:2,3
King James Version (KJV)

2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.
After the death of Sarah, Abraham took a third wife, her name Keturah.
Genesis 25:1-2
King James Version (KJV)

25 Then again Abraham took a wife, and her name was Keturah.
2 And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah.