Tuatha could be the elves that have long ago aligned with the humans or dwarves from old conquests. Like the elves in conqured retreats that live in wooden buildings and use metal weapons and armor. They are still immortal and generally quite intelligent, but they lack the physical prowess for hard labor in the mines or forges, they seek employment as guards, soldiers and clerical work. They should be the equalivent of the "high elves" or generic stereotype fantasy elf. Thuatha could be an insult akin to "traitor" or "tree-killer" or something in the Elven toungue that these wood-chopping, city building, civilized elves adapted to themselves out of spite for their nature-worshipping hippy ancestors. They should'nt form their own nations, peferring to live in the midst of other races.
Sylvan: I dunno. Name sounds "elfy" though
Trowe: These should be the Dwarf Fortress elves we all know and love. I imagine these guys are like the 'Liberal Crime Squad' transplanted into a fantasy realm. They are very much in touch with nature, to the point of extremism. They can speak to and form alliances with the animalmen, and even lesser animals and as such do not draw distinctions between sentient, civilized, or simple creatures, nor do they see any reason why they should, all creatures being equal in the eyes of nature. A human soldier they shoot down with an arrow in war is just as likely to be cooked over a spit as a wild deer bagged on a hunting trip. They are protective of nature, they consider the death a tree, with its long life span to be a signifcant loss, while animals with shorter lifespans to be porportionally less valuable. Since they are immortal, they look down just about everyone else and consider their culture the only one that makes sense or aligns with nature. They trade with other races and are generally friendly, if not overly condensending, like hippies, but can become aggressive and single-minded about transgressions against their ideals, like hippies. To them, if humans stick to their barren wasteland grasslands and dwarves to their mud and rocks, they are perfectly content.
Svart: Name makes me think of those Gaul, Celt or Germanic tribes from back in the day. Stark-naked and painted blue from head to toe screaming like mad-men weilding a two-handed sword. At a bit of a loss thinking up of multiple types of elves that are distinct enough to not just be lumped into one of the above.
Then again these are just rough ideas.