Those are some pretty toads! Anyway , red leg is usually widespread, looking kinda like a rash. Based on that picture that looks like some minor irritation, and it usually starts in the thigh/pelvis area. I wouldn't worry about red leg at this stage unless the redness starts spreading.
I'd like to see a picture of their enclosure if possible. You might be right about it being something about the environment. Only one of the toads is ramming the side of the tank?
That is so weird because its the same with my toads. The larger one consistently tries occasionally to escape, while the other doesn't do much, preferring to just relax most of the time, unless the larger one upsets her by trying to stand on top of her or jumps into her.