I thought that you stated before that you couldn't upgrade as big as you would like until you were out of the house? While that is a nice idea if you were 17 or 18 and planning on getting your own apartment off campus at college so you didn't have to worry about the rules with animals on campus (the typical rule is, underwater-breathing fish only and no bigger than a 10 gallon aquarium), you are only 13.
I know it's tough, but you have a responsibility to be a good turtle mom and in 5 or so years when you go off to college they will already be fully grown or nearly so and you are looking at either 4 100 gallon aquariums, or a pond. Do you really think that your parents will invest in that when they will not let you get anything bigger than what you have right now? Your brothers have turtles too? Then you definitely need a pond.
At 13, you are not in the position to suck it up and do the best you can for your turtles until you get out of the house because that is too long to make your turtles wait.
That being said, I think that you should SERIOUSLY consider re-homing at least 2 of your turtles (hopefully 3) and concentrate on giving the best life possible for 1 turtle until you have moved out of the house and can do whatever you want.
I know you want to do everything you can, but at your age, under your parents rules, you can't, and I hope you realize that.

