Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

I thought I saw an answer on this but can't find it now. Does Thaumaturge progress animal companion levels for druid/ranger/cleric w/ animal domain?

Also, does the Hierophant animal companion progression ability only work for Hierophant levels or does it progress animal companions for all classes?

No for Thumaturge, as for the Hierophant feat it adds your hierophant levels to your animal companion progression.

Thanks Valefort. At what progression levels do the companions level up? Assume pure druid for simplicity. Is there a final "level up" for the companions at druid 30? What level would the animal companion be? And with epic animal companion, it "levels up" one more time, correct? Then what level would the companion be?

Now, if I had 5 thaumaturge/10 hierophant (with animal companion progression)/15 druid and nature's bond along with epic animal companion, would my character's effective animal companion level be 31? What would be the animal companion's level be in this case?

Yes, effective animal progression would be level 31. You'd fall into the (30-32) bracket and your companion would be a level 21 beast. The last bracket is (33-35).

All these info can be found in the nwn2 wikia Aurali