Hi there----I worked at a shelter too! I was the cat lady (all the other volunteers were dog people). Can I make a suggestion (if you're still having trouble)? Start by mixing in a little food to their formula and mushing it together, really runny, and feeding them that out of the bottle. Little by little use more food, less runny, still from the bottle, and then finally start putting that mixture in a dish, then continue reducing the amount of formula until they're just eating the food.
Let us know how it goes, eh? My own furkids keep me going, that's for sure, so nice to hear about someone else's.
Rivergirl