First off, congrats! That’s a major score! 
I try to keep pets in places that must not take any damage, potential T4 crafters be damned. This would include indoors, on rooftops… anywhere that the purge is unlikely to appear save by some freak bug.
For thralls, I originally used steel trunches with blunt fittings all around until I encountered purges containing both humans and animals. It was a real chore being the only one who could kill anything, but after surviving, I decided to make some changes…
Initially, I tried practice swords with blunt fittings. This allowed the thralls to both KO humans and kill animals, but there was a problem. Humans with bigger KO bars than HP would still end up getting killed far too frequently. This was particularly true for archers I hoped to capture.
After thinking on the issue of needing thrall to kill animals but absolutely not kill humans, I decided to flip the problem on its head. Instead of blunting lethal weapons, why not increase the damage of truncheons?
Last purge, I put this to the test against An Outcast Vanir Chieftain. All fighters in the field (volcano & Sepermeru 1-handed T3s, plus several Dalinsias) were equipped with Steel Trunches with the highest grade weapon damage kit. T3 thralls wore Flawless Lemurian Warrior, the Dalinsias wore Silent Legion. There were no pets or archers used at all, but any 2-hand fighters (dancers, Seper Captains) I had were sealed inside or put on the roof and given blunted practice greatswords. (This is because during the prior purge, wolves and fighters spawned on the roof last wave, even though the base sits on flat ground.)
The result was that there were no accidental human deaths. The wolves took maybe 30 seconds each for the thralls to kill, and the Corrupted Wolf in wave 4 lasted maybe 2 minutes with half a dozen thralls wailing on it.
Overall, I’m quite happy with this setup and will be sticking with it for at least the next couple purges unless a future patch changes something.
Hope this helps…