To the OP, Have you reported this in any way to corporate? I work at a petco (in the grooming salon) and corporate, atleast in my district, takes that sort of thing pretty seriously. 3 care alerts on a managers watch and they get fired is the official policy. This would definitely be a care alert, heck maybe even two or three.
Here's a form you can fill out. There's also a phone number on that page.
I've never seen that happen at my store, and it doesn't actualy happen often in any case. So if it happened twice at the same time at the same place they must be doing something really stupid. Like not separating them for feeding, or forgetting to feed them all together