Is offspring in the Bible always used literally--that they're the literal offspring of the one who begot/birthed them? And of the exact same "species", so to speak?No--and neither are offspring of a different species than their Father:
Acts 17:29---King James Version
29 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man's device.
Hebrews 12:9---King James Version
9 Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the Father of spirits, and live?