Let me offer my comiserations, and your warning has definitely been taken on board. I am very, very sorry for your loss, I understand what it's like to be hurt by a family member.
From what I understand it sounds like this woman is being very spiteful, and I know what a disappointment it would be if one of my children turned around and did something like this. I'd feel like all those years of love, sacrifice and care would have been wasted, and that's no small thing.
The fact remains, however, that you loaned the snakes to your son. There is no grey area, and all the beaurecratic bs they spout makes no difference. Your son was the lessee, not this woman, it doesn't matter what address he is living at or has on his license, regulation dictates that upon changing his address he must do so for his license. Marital property laws are tricky, depending on the time they have been together, but if she has no interest in the animals and no ability to care for them properly she cannot keep them. A licensed keeper can have their animals removed for negligence, a licensed keeper can be done for wild-caught reptiles, and whether or not you loaned them to her of your free will a loan is a loan, and a verbal agreement is just that, and most likely is recorded as well. So theft is theft.
Your local authorities are being lazy and negligent, there is no such thing as 'civil service' these days, and that's what is depressing me about this.
I can't offer you advice, you're already doing all you can, but I can add my support, as small a thing as it is. I can tell you I know how you feel, and I can tell you that your warning has been taken on board. So you've made a difference here, I just hope things work out for you in the best possible way.
Good luck.