It seems to me that the introduction of nonhumans who aren't wolves introduced a break from the initial premise, and additionally it seems that all other nonhumans don't clearly have all of the attributes Holo and Myuri have, so I'd like some clarification.
From the initial story, Holo claimed to be a wolf, and she seemed to indicate kinship with other wolves. To be clear, she identifies mainly as a wolf, not a human, and her human form is treated as a guise. My understanding of this initially was that it indicated all wolves in this world were at human level intelligence, or at least smarter than normal animals, and might have the potential to take human forms. However, this assumption was probably wrong since there are shown to be avatars of birds, sheep, etc.
With regard to these other nonhumans, there seem to be differences to Holo. Firstly, Holo has the attribute of living in and having power over wheat (also, she is required to eat it to transform back into a wolf). I don't recall other nonhumans having any similar trait disclosed. Secondly, I haven't seen in the others the aforementioned kinship that Holo has for wolves. Our two sheep, for instance, are quite disrespectful to regular sheep. In volume 10 of Spice and Wolf,
we learn that the golden sheep has been eating sheep in order to fit in to human society.
Then in volume 3 of Wolf and Parchment, after offering to buy mutton for Myuri and Col, on page 188 Ilenia goes on to explain, "They look like kin, but in the end we're very different." These two, and Ilenia definitively, don't seem to view the regular sheep as their kin. In contrast to Holo, they don't seem to identify themselves as sheep (though they also don't identify as human).
Holo's attitude couldn't be any more different from these two sheep. In fact, on page 168 of volume 10 of Spice and Wolf, she throws up after learning that the golden sheep has been eating sheep.
Another point of note, the new Spice and Wolf: Spring Log books have introduced two new wolves: Selim and her brother Aram. What is the significance of these two being able to hide their ears and tails in their human transformations when Holo cannot? Is there a difference between these two and Holo or are they all the same kind of "wolf"?
So, for clarification, is Holo the same kind of entity as the rest of these nonhumans? Do these other nonhumans have powers over things like wheat but they keep their affinity secret, or do they lack these traits? Is the kinship Holo feels for the wolves merely a difference in attitude or does it indicate that she is a different kind of being?