Besides, she actually is my sister, the daughter of my father, but not the daughter of my mother; and she became my wife;
Genesis 20:12 (NASB)
When you read this plainly, it appears that Abraham and Sarah are half-siblings. However, the Hebrew is full of people using familial words to describe both close and more-distant relationships.
Much later, we'll see that Jacob refers to his "father Abraham," but he is talking about his grandfather, so this feels legitimate.
Then Jacob said, “God of my father Abraham and God of my father Isaac, Lord, who said to me, ‘Return to your country and to your relatives, and I will make you prosper,’
Genesis 32:9 (NASB)
So is Abraham really being honest here?
In a previous post, I said Sarah is described oddly at the top of the chapter; we can link the Abraham->Sarah relationship with Israel->Ark, where the ark is merely being used for victory. A stolen blessing.
Look closely at this next instance of misrepresentation to gain a blessing…
Jacob said to his father, “I am Esau your firstborn; I have done as you told me. Come now, sit and eat of my game, so that you may bless me.”
Genesis 20:19 (NASB)