I just inherited two Red Ear Slider turtles, they are three years old, but their tank is still pretty small..?

Hey...I have the same kind of turtle. I'm kind of to lazy to look at the link...but as long as the outside of the pool is hard and not tear-able (really strong beak on the turtles). The habitat being outside SERIOUSLY depends on what kind of climate you live in. If you live in the southern United States where is is warm year round...then that should be fine. Don't let rain get into the pool. Also make sure the water level is low enough so that they can't climb out of the pool. They are really good climbers, and are hard to find once they are loose (if they do get loose look in corners and dark areas). Also watch their behavior. I have only one turtle now, but a couple years ago I had two in the same tank, and one of them committed suicide by starving itself, because i refused to share food with the other turtle. Speaking of food i have noticed that the turtles prefer if you get floating food and put it in the water instead of somewhere dry. Hope this helps ( and that this wasn't to long). Any questions just ask. Hope you like your turtles and your turtles like you!!!