In this image, we can see clearly that Ptolemy II and Arsinöe II were called 'Siblings.' The Greek word for "siblings" is adelphoi - ΑΔΕΛΦΟΙ. This article about the incestuous marriages of the Ptolemies reads,
"On the reverse of coins dedicated to their parents as gods, they put their conjoined portraits with the added word 'siblings' (Adelphoi) -- just in case you missed the point. In fact, both king and queen took the title Philadelphos, 'Sibling-lover' -- used thereafter on documents and coins -- which deliberately highlights their incestuous union."
For some reason, there are those who claim that adelphoi means "brothers." But this is an image of a man and a woman.
Several couples in history and mythology were called Theoi Adelphoi - siblings gods - Cleopatra and Ptolemy, Zeus and Hera, Isis and Osiris, and Ptolemy II and Arsinöe II.