„The Symaethus is a river of Sicily, named after King Symaethus, not far from the city of Catania. Around it are the gods called the Palici, whose story is as follows. When Jupiter had violated the nymph Aetna—or, as some say, Thalia—and made her pregnant, fearing Juno, according to some he entrusted the girl herself to the earth, and there she gave birth; according to others he entrusted her offspring. Later, when two boys burst forth from the earth, they were called the Palici, as though ‘coming again’: for πάλιν ἵκειν means ‘to come again.’ At first they were appeased with human sacrifices, but later they were softened by certain rites, and their sacrifices were changed. Therefore the phrase ‘placable altar’ is used, because their divine power was thus softened. Varro calls the Palici gods of sailors. Others say that Jupiter, on account of Juno’s wrath, transformed this Palicus into an eagle. Others hand down that he was the son of Vulcan and Aetna.” (Servius, Commentary on Vergil's Aeneid 9.584)
Regardless of who the parents of these gods are, I prefer Aitna to be the consort of Hephaistos (the one impregnated by Zeus can be Thaleia, Hephaistos' daughter according to Stephanus of Byzantium) given his association elsewhere with both the nymph and the mountain:
„Etna is a mountain in Sicily, named after Etna, daughter of Heaven and Earth, according to Alcimus in his work on Sicily. Simonides says that Etna decided between Hephaestus and Demeter when they quarrelled over possession of the land.” (Scholiast on Theocritus 1.65); „And now, a helpless and a sprawling bulk, he [Typhoeus] lies hard by the narrows of the sea, pressed down beneath the roots of Aetna; while on the topmost summit Hephaestus sits and hammers the molten ore. There, one day, shall burst forth rivers of fire,with savage jaws devouring the level fields of Sicily, land of fair fruit—such boiling rage shall Typho, although charred by the blazing lightning of Zeus, send spouting forth with hot jets of appalling, fire-breathing surge.” (Aeschylus, Prometheus Bound 365-74); „Nor can I any more respect that other story, though it is more reverent in its tone, to the effect that Hephaistos attends his forge in Etna, and that there is there an anvil on which he smites with his hammer.” (Philostratus, Life of Apollonius of Tyana 5.16); „When Zeus struck Typhon with a thunderbolt, Typhon, aflame hid himself and quenched the blaze in the sea. Zeus did not desist but piled the highest mountain, Etna, on Typhon and set Hephaestus on the peak as a guard. Having set up his anvils, he works his red hot blooms on Typhon's neck.” (Antoninus Liberalis, Metamorphoses 28).