OK, your kittens are about what ... 4 to 5 weeks old now? Are they eating the moist kitten food consistantly now? Do they still take any interest at all in the bottle? How about litter activities? Are they eliminating on their own or are you still stimulating them?
Sorry for all the questions in response, but it helps me to know where the babies are in terms of maturity.
OK, then I think you can probably taper down on the bottle and offer a dish of water. Once they are drinking it on their own, stop bottling them completely - you might want to place the dish where you won't mind mopping it up until they get used to it. Also, make certain you put it in a flattened dish because until they get the general idea, they can easily fall into it and that wouldn't be good.