Iscah is the child of Haran
And Abram and Nahor took them wives: the name of Abram's wife was
Sarai; and the name of Nahor's wife, Milcah, the daughter of Haran,
the father of Milcah, and the father of Iscah. (Genesis 11:29, KJV)
The first thing to understand, before other determinations are made, is where Abram and Nahor and Haran stand in relationship and age to each other. It is true that Abram is listed first among the sons of Terah.
Haran is Abram's brother
And Terah lived seventy years, and begat Abram, Nahor, and Haran.
(Genesis 11:26, KJV)
Who is older?
Being listed first does not establish that Abram was born first. Regardless of age order, sons which are in the line of Christ, those receiving the spiritual birthright, are typically listed first. Jacob and Esau is a prime example: we know that Esau was the firstborn, yet the Bible lists Jacob first.
25> And the first came out red, all over like an hairy
garment; and they called his name Esau. 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. (Genesis 25:25-26, KJV)
And Isaac sent away Jacob: and he went to Padanaram unto Laban, son of
Bethuel the Syrian, the brother of Rebekah, Jacob's and Esau's
mother. (Genesis 28:5, KJV)
And I gave unto Isaac Jacob and Esau: and I gave unto Esau mount
Seir, to possess it; but Jacob and his children went down into Egypt.
(Joshua 24:4, KJV)
By faith Isaac blessed Jacob and Esau concerning things to come.
(Hebrews 11:20, KJV)
The sons of Noah are also listed out of order, placing Shem, who was younger, first.
And Noah was five hundred years old: and Noah begat Shem, Ham, and
Japheth. (Genesis 5:32, KJV)
And Noah begat three sons, Shem, Ham, and Japheth. (Genesis 6:10, KJV)
Nothing in the Bible indicates that Noah's three sons were triplets. In fact, that Shem was not actually born when Noah was 500 can be established based on Noah's and Shem's respective ages at the time of the flood.
And Noah was six hundred years old when the flood of waters was upon
the earth. (Genesis 7:6, KJV)
These are the generations of Shem: Shem was an hundred years old, and
begat Arphaxad two years after the flood: (Genesis 11:10, KJV)
So, Noah was 600 years old, and Shem was 98 years old at the time of the flood. This means Noah was 502 when Shem was born--simple math. Then who was the oldest, the one born when Noah was 500?
Unto Shem also, the father of all the children of Eber, the brother of
Japheth the elder, even to him were children born. (Genesis 10:21,
KJV)
Japheth was the eldest. (Note that some Bible translations make a mess of this fact--perhaps because the translators assumed Shem should be the eldest; but the KJV is correct.)
Abram was younger than Haran
Back to the case of Haran and Abram: Abram was the younger. Just as Noah's age was said to be 500 when he had his three sons, the age listed being Noah's age at the birth of the first son, Terah's age is given only as at the birth of his firstborn.
And Terah lived seventy years, and begat Abram, Nahor, and Haran.
(Genesis 11:26, KJV)
And the days of Terah were two hundred and five years: and Terah
died in Haran. (Genesis 11:32, KJV)
So Abram departed, as the LORD had spoken unto him; and Lot went with
him: and Abram was seventy and five years old when he departed out
of Haran. (Genesis 12:4, KJV)
According to the Biblical record, Abram departed from Haran just after his father had died. Terah died at the age of 205, and Abram's age at that time is recorded as being 75. This means Abram was born when Terah was 130 years old. If Terah's firstborn came at age 70, there is a period of 60 years intervening between the first and Abram--who must be the last.
This means Haran, depending on whether he was the firstborn or the secondborn, may have been as much as 60 years older than Abram, and well within range of fathering a daughter who was but ten years younger than Abram.
Who is Sarai/Sarah?
Haran being older than Abram does not mean that Iscah and Sarah are one and the same; it only strengthens the possibility.
But Abraham's own confession as to Sarah's identity should put to rest any notion that they are the same.
11 And Abraham said, Because I thought, Surely the fear of
God is not in this place; and they will slay me for my wife's sake.
12 And yet indeed she is my sister; she is the daughter of
my father, but not the daughter of my mother; and she became my wife.
(Genesis 20:11-12, KJV)
So Sarai/Sarah is Abraham's half-sister. This cannot possibly have been a daughter of Haran, who would have been his niece. This just shows, once again, how easily even the writers of commentaries can be led astray if they are not thoroughly knowledgeable on the subject upon which they are writing. Many commentarians make unwarranted assumptions.
Conclusion
Assuming Iscah is a daughter, she would be the daughter of Haran, and Abram's niece: but Abram did not marry a niece; he married a half-sister. Therefore, Iscah and Sarai cannot have been the same person.
