>According to the scheme in lesson 2:
>
> s. pl.
>nom. stem+r stem+ar
>
>the word for fire would be:
>
> s. pl.
>nom. eldr eldar

This is correct.

The complete scheme:

sg. pl.
nom. eldr eldar
acc. eld elda
dat. eldi eldum
gen. elds elda

Regards,
Haukur