Your turtles are over 6 years old?? and only 2.5?? I don't think that's normal...?
Anyway, your tank is to small. You need a way way way bigger one! Putting 3 turtles of that size in a 10 gallon is a very bad idea.
You need over a 60 gallon, not considering upgrades.
Other than that you're doing alright. The filter will need to be cleaned every day or it won't work lol. Turts are messy. Also, you want to put as much water as you can!
My dock for Bobbi is a stick on one and it's at the very top of the tank so her tank is over a third of the way full.
I wouldn't worry about making your tank pretty. Turtles enjoy river rocks, they play with them and it adds something.
I tried fake plants at first but my turtles tore them to shreads.
