From the size of them, I'd venture to guess that they are around 3.5-4 weeks old. Cute!!!!!!!!!!!
At around 4 weeks, they do start munching on some wet food, or wet food formula slop (formula and wet kitten food mixed together). I wouldn't altogether stop the bottle feedings with these little ones yet. I would bottle feed twice a day, and offer the "slop" once every 2 hours or so, to get them accustomed to the texture, and to eating, rather than suckling. Week by week, you can reduce the amount of formula in the slop, so that they're just eating straight-up wet kitten food. I would leave dry kibble out for them, if you wish...some begin experimenting with crunching on this on their own. Leave a water dish out at all times...shallow, however. They'll get the hang of this on their own. How about litter training...how's the potty situation?