[Legolas]

From Unfinished Tales:

The earlier story (apart from the question of the ban and the pardon), to which the statements in The Silmarillion, The Road Goes Ever On, and Appendix B to The Lord of the Rings refer, is fairly clear: Galadriel, coming to Middle-earth as one of the leaders of the second host of the Noldor, met Celeborn in Doriath, and was later wedded to him; he was the grandson of Thingol's brother Elmo – a shadowy figure about whom nothing is told save that he was the younger brother of Elwë (Thingol) and Olwë, and was "beloved of Elwë with whom he remained." (Elmo's son was named Galadhon, and his sons were Celeborn and Galathil; Galathil was the father of Nimloth, who wedded Dior Thingol's Heir and was the mother of Elwing. By this genealogy Celeborn was a kinsman of Galadriel, the grand-daughter of Olwë of Alqualondë, but not so close as by that in which he became Olwë's grandson.)

In Doriath she met Celeborn, grandson of Elmo the brother of Thingol.

These are the only mentionings of Elmo in Unfinished Tales. Celeborn was, indeed, his grandson.

I'm not finding any reference to Oropher coming from Doriath. It can be speculated, I suppose, but nothing in Unfinished Tales confirms it. His name only appears in the Appendix B that I uploaded/added a link to and in footnote 14 for the Gladden Fields chapter:

14 - Long before the War of the Alliance, Oropher, King of the Silvan Elves east of Anduin, being disturbed by rumours of the rising power of Sauron, had left their ancient dwellings about Amon Lanc, across the river from their kin in Lórien. Three times he had moved northwards, and at the end of the Second Age he dwelt in the western glens of the Emyn Duir, and his numerous people lived and roamed in the woods and vales westward as far as Anduin, north of the ancient Dwarf-Road (Men-i-Naugrim). He had joined the Alliance, but was slain in the assault upon the Gates of Mordor. Thranduil his son had returned with the remnant of the army of the Silvan Elves in the year before Isildur's march.

The Emyn Duir (Dark Mountains) were a group of high hills in the north-east of the Forest, so called because dense fir-woods grew upon their slopes; but they were not yet of evil name. In later days when the shadow of Sauron spread through Greenwood the Great, and changed its name from Eryn Galen to Taur-nu-Fuin (translated Mirkwood), the Emyn Duir became a haunt of many of his most evil creatures, and were called Emyn-nu-Fuin, the Mountains of Mirkwood. [Author's note.] – On Oropher see Appendix B to "The History of Galadriel and Celeborn;" in one of the passages there cited Oropher's retreat northwards within the Greenwood is ascribed to his desire to move out of range of the Dwarves of Khazad-dûm and of Celeborn and Galadriel in Lórien.