Elven or Elfin? [duplicate]
The choice is yours:
If you want elves like Tolkien’s, use Elves and Elven and Elvish.
If you want elves like Wolfe’s, use Aelf (plural Aelfe) and Aelfinn.
If you want elves like Andrew Lang’s or Walt Disney’s, use Elfs and Elfin and Elfish.
The first is English, the second Nordic, and the third Tinkerbelly.
Names matter.
(I decided to make this an actual answer instead of a comment, since the OP didn't feel it was adequately covered in the question I tagged as a duplicate, When to use "Elven", "Elvish" and "Elfic"?).
Following influential author JRR Tolkien, the "v" spelling is generally considered more "serious", the "f" spelling more whimsical. There is no difference in the grammar.