Wish I could help you properly with the problem. It is quite a while since I've played AHC the last time and even then it always took quite some time till I found all of the dens.

Some general advice though, maybe it helps:
As far as I remember there is a way to approach the running water there from both sides all the way through. So maybe if you're hearing the wolves near to the water they might actually be on the other bank?
Also always search for small openings in the underbrush. Try to make a full circle around the sound source and maybe you find a small gap where you can enter an otherwise cut-off part of the map.
So yeah, this quest, even with the bugfix for the sound panning of the wolf sounds, was one of the more time consuming for me.
Btw make sure you're playing on the most recent version. As mentioned there was a version where the wolf sounds didn't pan correctly and it was really difficult to find the dens by ear. But as you're playing probably way more than a year after the patch you've most likely already have that fixed version.