This is the genealogy of Terah: Terah begot Abram, Nahor, and Haran. Haran begot Lot.
And Terah took his son Abram and his grandson Lot, the son of Haran, and his daughter-in-law Sarai, his son Abram’s wife, and they went out with them from Ur of the Chaldeans to go to the land of Canaan; and they came to Haran and dwelt there.
Then Abram took Sarai his wife and Lot his brother’s son, and all their possessions that they had gathered, and the people whom they had acquired in Haran, and they departed to go to the land of Canaan. So they came to the land of Canaan.
So Abram said to Lot, “Let’s not have any quarrelling between you and me, or between your herdsmen and mine, for we are brothers.” (NIV)
The apparent contradiction comes from the translation of the Hebrew word awkh. This word can mean brother, half-brother, relative, partner, or something with a resemblance. As in our language, the contexts in which words are used determine their meaning. The clear passages lay out the genealogy of the son’s of Terah. Genesis 11:27 makes it clear that Lot is Haran’s son, not Terah’s. This is confirmed by verse 11:31 and 12:5. The apparent conflict comes when Abram appeals to Lot on the basis of their close relationship. He refers to Lot as a brother, but his appeal is to their bond as close relatives.
Even in our culture, the term brother is used to represent people with a bond through civic clubs and military service. Paul referred to Timothy (as well as many other believers) as a brother (e.g., 2 Corinthians 1:1; Colossians 1:1). Indeed, that term applies to all believers—we are brothers and sisters in Christ. If one were to have a brother (sharing mother and father) who has not repented and put his trust in Christ for salvation, he would not be a brother in Christ. Depending on the context, he would be both a brother and not a brother.
The context makes it clear that Lot was both Abram’s nephew and his brother: his nephew by actual relationship, yet a brother as a member of the family of Terah.