I don't know, but I think you are misunderstanding what is being said.
Apollo is a male god.
Artemis is a female goddess.
Artemis is the elder twin sister of her brother Apollo.
Yes, Apollo had a twin sister named Artemis.
Apollo's twin sister is Artemis. Athena is their half sister.
Was Artemis the twin sister of Apollo.
Yes, he had a twin sister named Artemis (Artemis was older).
No; Apollo's only twin sister is Artemis.
No, Apollo's twin sister was Artemis.
Apollo has a twin sister, Artemis, the chaste huntress.
No, a twin sister: Artemis.
Apollo had one twin sister. Her name was Artemis.
He had a twin sister named Artemis. She was the goddess of the Hunt and the moon.
Artemis is the (older) twin sister of Apollo.
Apollo has only a twin sister: Artemis.