Time for a little artist insight!
Here’s an interesting test for anyone who enjoyed RubyQuest:
Re-read the quest. Look for any mention of “cat”, “fox”, “bunny”, “ear”, “tail”, “snout”, or anything like that.
You won’t find it.
For instance, when Ruby meets Red, he’s described as “the man”.
The characters in NanQuest, as in RubyQuest, were primarily given their animal identities as a means of visual shorthand, not literal personification. The ears are a way to easily tell the characters apart and give them some personality. Whether or not Ruby is literally a rabbit girl is not significant to the narrative. Ruby never uses her bunny jumping power, Ace never flies like a bird, Filbert never stuffs seeds in his cheeks. There may be, in both quests, some symbolism or connotations to these choices, but every character could be a human and it wouldn’t change much. This is by design.
Initially I thought to differentiate the characters by giving them all different hats. But there’s an obvious flaw here: Hats can be removed or switched. I needed a more definitive way to prove a character was a character, and not just wearing someone else’s hat. Thus the ears. Now you know!
To answer your question more directly however, while RubyQuest had simple and direct animal analogues, NanQuest is less obvious (other than Nan herself who’s pretty obviously a goat). This is largely because NanQuest has a significantly bigger cast, and because reusing obvious animals like cats would make people think they were RubyQuest cameos.
As a result, while I do have certain animals influencing the design of given characters, they’re not really important. So large speech aside, here’s your concise answer: It doesn’t matter. Just draw whatever you think they should be!