In every text that I can recall, with one exception, the term refers either to the land or to the physical descendants of Abraham, Isaac, and Jacob. We cannot say only Abraham's descendants, because the Ishmaelites also claim Abraham as their progenitor. Ishmael was Abraham's son by Hagar, his wife's Egyptian slave.
Isaac was the son of Abraham's wife, the free-woman, Sarah. His son Jacob became the father of twelve sons who, in turn, became the heads of the twelve tribes of Israel. Palestine was, for them, the Promised Land, i.e. the land promised to Abraham and his descendants, and confirmed to Jacob. It was the land of Israel.
The one exception is Galatians 6:16, a reference to "the Israel of God." Commentators disagree on interpretations of that expression, some believing that it refers to all born-again believers, others that it refers to Israelites who accepted Jesus as the Messiah of God. The second opinion is, in my judgment, the correct interpretation.