Your tank IS big enough for 2 but, like I said, males can be aggressive. You can sex them by looking at the dorsal fin which is longer and pointed in males, and the body shape as females are deeper-bodied and, when viewed from above, wider. If you have 2 males, even in this size tank, you could still encounter some disputes once they reach sexual maturity - mainly due to their size which also means they have a larger territory in this case. They will be bigger than anything else in the tank and whether or not the tank is large enough (it's around 65 gallons BTW), they will still eventualy eat any small fish like neons like I said before (actualy, angels also eat neons). As the tank is as large as it is, depending on the number of angels you have and the sexes of the gouramies, you probably be able to get away with keeping them together but you will have to look into re-homing any very small fish (you didn't say what kind of tetras you have).