Turtles are great, amazing wee fellas to watch but do require a huge tank, I've had yellow bellied sliders in a 5ft tank and to be honest, it was too small, I did rehome them to a friend who made a dedicated turtle tank that was 15 ft in length and access to a land area rather than a floating dock. I took on more as someone was going to throw them in the bin and my friend also has them now. I think you need the huge tank prior to getting them, the first two I got were given to me along with the tank so I always had the intention of passing them on.
Think long and hard before you go ahead with getting them.