If you took them from the wild they may not get along with each other for a long time. They don't hang out together like Ninja Turtles. They can learn to tolerate each other but I wouldn't leave them alone together. They can bite and flip each other over. Start by feeding them together. That will keep them focused on something other than knocking the snot out of each other. Let them out of their cages for walks together, see who gets along with who and when.
You can try out an outdoor pen with minimum measurements of 4 feet by 8 feet. As long as you have created enough space, the turtles are less likely to fight each other. You can make a wire fence in the pen and separate the turtles that seem like they're fighting.
I wish answering your question this is what i think.. Put them in each a cage they wont see each other if they keep fighting or one of them have a red mark consult an animal doctor or a zoo animal doctor something like that.