I've been making some progress with the Cuitzeos at feeding time.

Lacrimosa is a voracious feeder, always has been. She just needs to get a whiff of food and she's out looking for it. I've decided that I want to use food (one of her base instincts) to build up more trust between us. So I want her to be quite clear that it is ME that provides her food, and not the metal tongs. She reacts to the tongs, so I figure I need to use them in a way that the realises that I am attached to them. Previously I'd start pulling away if she worked her way up the tongs sniffing, now I let her sniff up the tongs all the way to my fingers, she seems to know that they aren't food.
I've also started getting her to come up to the bottom of the open doors to receive some of her food. At the moment I'm still having to tong feed her a piece to get her feeding response going, then draw her over to the doors with another piece. Last night she stayed with he head resting on the bottom lip of door for three successive pieces of fish/pinky. I'm hoping with time she'll start coming to the front when she smells food.

The final success last night is that I want them to associate my hands with good things (i.e. food) and decided on a slightly risky strategy. I put my hand in the viv and hled the food on the other side of my hand, so that the easiest way to reach the food was to use my hand as support... there was the risk of a bite here, given Lacrimosa's enthusiastic feeding response, but I did get both her and Vlad to rest on my hand to feed - the food was about 10cm from my hand, so far enough that they shouldn't confuse the scent. I had a hairy moment when I had Vlad resting on my hand and Lacky started "nosing" my little finger, I know this is one of the things Vlad does when he's preparing to eat a piece of food (but Lacky has usually struck at it from several inches away) so I braced myself for a bite that never came.

On the whole Vlad is a more nervous feeder, he prefers feeding near his hide. However, this is a good thing as he had stopped eating before we put him back in with Lacky, so seeing him feeding at all is a good thing. He's miles behind the learning curve that Lacky is on, but I'm sure he'll come around.

Their next feeding should be interesting, I'll be continuing the same sort of reward-based feeding.