Gen. 11:29 states:
And Abram and Nahor took themselves wives; the name of Abram's was Sarai, and the name of Nahor's wife was Milcah, the daughter of Haran, the father of Milcah and the father of Iscah.
In his Genesis commentary, Rashi states that Iscah is Sarah. But when Abram (Abraham) passes Sarai (Sarah) off as his sister instead of saying that she's his wife, he later elucidates that Sarah is his half-sister (he says this to King Abimelech in Gen 20). Sarah and Abraham have the same father (Terah) but different mothers.
And Haran is Abraham's brother (Abraham's brothers: Nahor and Haran). So if Gen 11:29 describes Iscah (who Rashi says is Sarah) as being Haran's daughter, then that would make Sarah Abraham's niece, not his half-sister, right?
What's going on here?
Also, Sarah being both Iscah and Sarai would mean that she underwent a name-change two times instead of one? God changed her name once from Sarai to Sarah, but her being tied to the name Iscah suggests another name change? What are some insights about this?