They're for children or young adults (given some of the themes in some of the books, I would say late preteen is loosely the right age group.) I don't really understand why that's relevant though? As t
he Wikipedia article notes, Jacques' work has been favorably compared to LotR,
The Wind in the Willows (another popular, successful book that has extremely few human characters), and
Watership Down (an actual xenofiction book...which also shows the harsh limits that true xenofiction imposes, even when focused on real Earth animals.)
What does "cultural grounding" refer to? I'm unclear on that, and without it I can't really respond to this.