Ke... kaw'it.

[wm.annis]

I've been thinking that fra- means "every", rather than "all"--at least partly because the nouns it attaches to are in the singular, although this might just be my English bias showing up. 

Well, from the standpoint of just numbers, "each" and "all" are identical: "every human being on the planet" vs. "all human beings on the planet" — it's the same number of people.  But "every" conceptualizes them as individuals, "all" as a whole.  Linguists speak of "distributive" and "collective" senses here.  Some languages have both distributive and collective plurals.

Given Frommer's free use of nìwotx "all (of), in toto," (5 times in the Corpus) I'd guess he sees Na'vi's plurality markers (both ay- and things like fra-) as more toward the distributive range of senses, with nìwotx shifting towards the collective senses.