It is important to do research before u get a baby turtle - if their setup is inadequate they can get sick very easily. You will also need to have plans to separate ur turtles in due time. Turtles r not sociable animals & when housed together they can fight & even kill each other for territorially purposes.
*One turtle alone needs a 120+ gallon tank
*They need a canister filter - this is very important in maintaining a turtles health - I would recommend the Rena Filstar XP3 or XP4.
*You need a water heater & keep the water temps around 78-80.
*You would need a basking area with the basking temps being 10 degrees warmer than the water temps. The basking area needs a heat light as well as a separate UVB light over the basking area.
*For feeding u should feed vegetables, live plants (anacharis, hornwort, duckweed, frogbit), & protein (pellets, fish, snails, crickets). Feed every day when they r younger than a year old.. once older than a year than switch to every other day. As a baby 50% of their diet should be vegetables, when they r adults it should be 75%.
It is important not to include gravel in the tank as ur turtle can become impacted & would need to seek medical attention.
It is also important to raise the water level as high as u can without allowing ur turtle to escape. If ur turtle is not used to swimming in a lot of water u can gradually raise the water level every few days until they get strong enough to swim naturally. Aquatic turtles r meant to swim & need all the space & water they can get!
As for sexing them right now they r too young. Once a turtle matures u can tell the difference between them very easily. The males will have long front nails & a long thick tail. Females will have short nails & a thin tail.
Good luck to you!