Males tend to fight each other. Of course, box turtles are individuals, too, and you might not have any problems, but I'd put money on there being problems with two males in close contact with each other. I've had some brought into rescue that had the marginal scutes over the neck worn down by the "attentions" of a more dominant male - same thing happens to lone females kept with a male, or females kept in too close of contact all the time with a male.

Katrina