The term "sister wife" occurs in ancient Greek literature, in reference to a woman who is both a wife and a (full-or-half) sister of her husband, but my question is in regards to Greek mythology: Who had a sister wife?
In the theogony found in Hyginus’ Fabulae, Caligine, “Fog,” gives birth to Chaos and then marries him. Their son Erebus, “Darkness,” then marries his own sister Nox, “Night.” Erebus and Nox then have a son Aether who marries his own sister Diēs, “Day.” Caelus, “Sky,” and Terra, “Earth,” are the son and daughter of Aether and Diēs. They too become each other’s spouses and produce numerous sons and daughters, almost all of whom marry one another.
The Fabulae is a Roman version or interpretation of Greek myths, with the Greek names more or less swapped out for Roman ones. Hyginus’ theogony differs on various points from the much more ancient text actually entitled Theogony written by Hesiod.
Caligine, the thick mist of darkness from which Chaos emerged, does not seem to correspond to any very obvious Greek counterpart, but Chaos = Khaos; Erebus = Erebos; Nox = Nyx; Aether = Aither; Diēs = Hemera; Caelus is Ouranos [Uranus]; and Terra is Gaia.
In Hesiod’s Theogony, Erebos, Nyx and Gaia are born out of Khaos, or they simply emerge afterwards from the same universal nothingness that at first engenders Khaos. Gaia then gives birth to Ouranos and to Pontos (the Sea), and she consorts with both of these sons of hers. Hesiod’s and Hyginus’s accounts of the children of Ouranos/Caelus and Gaia/Terra correspond fairly closely from this point on in the shared chronology.
Ouranos and Gaia had twelve children called the Titans, six male and six female. Of the six male Titans the only one who did not marry a female Titan is Kreios [Crius], who married his own half-sister Eurybia, a daughter of Pontos and Gaia.
Each of the rest married a full-sister of his own, specifically: Okeanos [Oceanus] married Tethys; Koios [Coeus] married Phoibe [Phoebe], Hyperion married Theia; Iapetos married Themis (although there are versions in which Iapetos’ wife was his own niece, a daughter of Okeanos); and Kronos [Cronus] married Rhea.
The sea-god Phorkys [Phorcys], a son of Pontos and Gaia, married his own sister, the sea monster Keto [Ceto]. They are best known as the parents of the Gorgon Medusa.
The river Inakhos [Inachus], a son of Okeanos, married his own sister Melia. One of Zeus’s earliest consorts Io, the mother of Epaphos, was one of their children.
Zeus, the king of the gods, was a son of Kronos and Rhea. According to Hesiod’s Theogony, he was married six times to different relatives (almost all cousins and aunts) of his before settling down with his seventh wife Hera, who was his own full-sister. The fourth in the series of wives, Demeter, was also a full-sister of his (as per Lines 912-914). It is from their union that Persephone, who grows up to marry her uncle Hades, is born. In the Orphic version of this story (as alluded to by Daniel Ogden in Drakon: Dragon Myth and Serpent Cult), Zeus’s mother Rhea threatens Zeus in the form of a dragon. Zeus likewise transforms into a dragon in retaliation and rapes Rhea, who is mystically identified with Demeter. It is in this fashion that Persephone is produced, who is thus, actually, a half-sister (as well as a niece) of her husband Hades.
Zeus had a son named Tantalos [Tantalus] whose mother was a nymph named Plouto [Pluto]. According to Hyginus, Plouto’s father was called Himas. The Scholia on Euripides’ Orestes and on Pindar’s Olympian Ode 3 say that Plouto’s father was either a certain Himantes or the Titan Kronos. It might be that Himas and Himantes are names of Kronos. In his encyclopaedia article of the Plouto personage, Aaron Atsma notes the following:
Nonnus appears to identify Plouto with the Phrygian goddess Kybele (Cybele), attaching the Kybelian epithet Berekyntia to her name. Indeed, Mount Sipylos, the home of Plouto, was a well-known cult centre of Kybele.
One ancient scholiast calls Plouto a daughter of Kronos (Cronus) clearly identifying her with Demeter, the goddess of agricultural prosperity (plouton). Demeter was also sometimes identified by the Greeks with the Asian Kybele.
An Okeanis Nymphe named Plouto also appears in the lists of Hesiod. It is unclear if she was connected with Plouto the mother of Tantalos.
In his Dionysiaka, Nonnus calls Plouto the bride of Zeus, implying a marital union at some point in time between Zeus and Plouto. If Plouto is to indeed be understood as Kronos’ daughter, then she would have been Zeus's sister (or at least half-sister) as well as his wife.
In his Bibliotheka Historika, Diodorus Siculus says that Iasion, son of Zeus and Elektra, was married to Kybele. Pausanias says that Kybele was the daughter of the Phrygian sky-god Dios, whom he calls Zeus, by the earth-goddess, whom he identifies with Gaia.
Quintus Smyrnaeus’ Fall of Troy cites Enyo, a sort of female version of Ares, as the sister of this war-god. The associations between Ares and Enyo may be intended merely as symbolic but certain hints among them imply that they were married to each other. Enyalios is either the son of Ares and Enyo or is merely a title of Ares.
At different points in time, Ares’ brother the fire-god Hephaistos [Hephaestus] was married to two half-sisters of his. The first is the love-goddess Aphrodite, daughter of Zeus and Dione (although there is a more dramatic version of her origin, in which she sort of doesn’t have any parents). After the divorce between Hephaistos and Aphrodite, the fire-god married one of Aphrodite’s sidekicks, Aglaia, who was one of the three Kharites [Charites], “Graces,” daughters of Zeus and Eurynome. Hephaistos himself was either the son of Zeus and Hera, or Hera gave birth to him without the assistance of male seed. In the latter instance, then, he would be the brother of neither Aphrodite nor Aglaia.
Aphareus was the son of Perieres (son of Aiolos [Aeolus], son of Hellen, son of Deukalion [Deucalion], son of Prometheus, son of Iapetos) by Gorgophone, daughter of Perseus the Gorgon-Slayer. After his father’s death, Aphareus’ mother Gorgophone became, according to Pausanias’ Description of Greece 2.21.7, the first woman ever to remarry. Arene was the daughter of Gorgophone by her new husband Oibalos [Oebalus]. When they had grown up, Aphareus got married to his half-sister Arene. Idas and Lynkeus [Lynceus], who became notorious as rivals of their kinsmen the Dioskouroi [Dioscuri], were the sons of Aphareus and Arene.
Herakles, the son of Zeus by Alkmene (a niece of Gorgophone), after he died and became a god on Mt Olympos [Olympus], was married to his own half-sister Hebe, a daughter of Zeus and Hera.
Zeus, as his wife Hera was also his sister. They were carrying on family tradition, as their parents, Cronos and Rhea, were also siblings, while their parents Ouranos and Gaia varied the formula: he was her son.
I was surprised to see that as far as I can tell, none of the other major Greek deities got together with their siblings, except for Poseidon, who raped his sister Demeter, and Hephaistos, who tried to do the same with Athena.