OT question about elves

[Alneyan]

Orcish is the only adjective form I ever heard for Orcs; there is the occasional Dwarfish for Dwarves, but Dwarven is a lot more common.

Make your own choice for Elves: Elven, Elvish, and Elfin are relatively common, with Elven being the most widespread, and Elfin rather common in lighter writings.

Still, you can get away with making up your own adjectives: Tolkien did just that, and created some new plural forms, if memory serves. Some names have so many variations it isn't even funny: Morgan/Morgana/Morgane/Morgain/Morgaine La/Le Fey/Fae (and a couple of others, including Fée or Fee perhaps, or even Fata), and other such names where spelling varies wildly.