Question: Does the Bible ever use the word “brother” or “sister” for more distant relatives?
Answer: Nieces and nephews were definitely sometimes called brothers and sisters. For example, Lot was Abraham’s nephew and Sarah was his niece (based on identifying Yiscah with Sarai and her father Haran with Abraham’s brother Haran in Gen.11:29), but Abraham refers to Lot as his brother (Gen.13:8,14:14), and told various kings that Sarah was his sister (Gen.Chs.12 and 20), Isaac and Rebekah were cousins once removed (Rebekah’s father Besuel was the son of Abraham’s brother Nachor, so he was Isaac’s first cousin; see Gen.22:23), so when Isaac tells the Philistines that Rebekah is his sister (Gen.26:7), he is referring to his cousin as his “sister”.
All the Best, Rabbi Azriel Schreiber