Hello! Another question. The word Atanatari – and we have Atanatarion. How do you form this word from the plural "half-elves"? I mean peredhel + ion or peredhil + ion? Is it Peredhilion?
Atanatarion is the genitive plural of Atanatar - and both are in Quenya. Peredhel, meanwhile, is in Sindarin, so you cannot apply Quenya morphology to it. Do you want this in Quenya, or in Sindarin?
Something I just remembered - Tolkien actually gave us what is essentially the Sindarin equivalent of Atanatárion as the title of a part of the Silmarillion - Nern in Edenedair (lit. "Tales of the Fathers of Men"). So if we follow this example more closely, we can also go for Nern i Pheredhil.