Briareus sibling Gyges
Principal sources
The Theogony
According to the Theogony of  Hesiod, Uranus (Sky) mated with Gaia (Earth) and produced eighteen children.  First came the twelve Titans, next the three one-eyed Cyclopes, and finally the three monstrous brothers Cottus, Briareus and Gyges. As the Theogony describes it:
brother or sister kin