I'm in the same boat with my new girls at the moment!
It can take some time to get the hang of the bottle. Make sure, it's always fillled to right to the top, so the water pressure keeps the ball pushed close. You can try and push the ball with your finger to show them the sound they should make when your piggies are comfy with you around. Change the water in the bowl at least once, better twice daily until you KNOW they have figured out the bottle.
Some pigs never get the hang of it or plainly refuse to drink. In those cases make sure they're getting some veg with high water content morning and evening (eg. cucumber, melon or celery, fresh hand-cut grass). Guinea pigs in the wild survive without constant access to water, getting most of the water intake from their food.
As long as your piggies are not drinking properly, monitor their pee (Is it concentrated and dark yellow?) and their fur (Is it waxy and dull?). If the answer is yes, they're not getting enough fluid and you need to adjust their food.
