there can be only one

What is the Latin plural of Elvis?
I’ve just seen Elvii, which is clearly wrong (the singular would then be Elvius).
The most obvious candidate is Elves, but of course one cannot count on one’s readers to pronounce it with two syllables.
On another hand, maybe it’s a consonantal stem, with a plural such as Elvires, Elvites or Elvides. The existence of the feminine form Elvira (no pun intended) suggests the first of these.
(In each of these the last /e/ is long.)