once living things are living things that once lived but dead now
Greg once lived out there in the desert.
I once lived with my best friend.
The correct phrase is "Greg once lived out there in the desert." "There" indicates a location or place. "Their" is used to show possession, and "they're" is a contraction for "they are."
he once lived
once there lived or once upon a time
having inhabitants; occupied; lived in or on: an inhabited island.
a french nobleman who lived a life of luxury in France
Yes! He has lived in Virginia once.
To introduce once again.
Once upon a time, there lived a lonely but kind old man in a small village.
annual
Published once a week.