Unless ya catch em in the act it'll be almost impossible to tell the genders apart from one another untill they get to around hand size. Once they are that big it becomes a tiny bit easier but only due to the male growing out a kok while the female will just get boxier over time. With your 2, they are still to small to sex them properly. Granted tho, if they aren't trying to kill each other that's a pretty good sign they have paired up lol.