As Lupin said, males will have bristles around the whole snout area. At 3-4", if you had a male I would think some small, short bristles would already be showing.
Two females may hunch their backs at each other and basically try to "bully" the other female away from a piece of food just dropped in. This is harmless behavior. Just being selfish over food.
A male and female adult within a couple of months of spawning age will interact more, he'll chase her away from him. Harmless behavior.
Two males are usually fine together in a tank as long as there are no females to fight over for breeding rights. They may to the hunching up of their backs at each other over a piece of food, but they won't hurt each other over it. Two males in a tank do like to have their own hiding places, so they can be out of view from the other one when they want to. So you should provide hiding spots on both sides of your tank....can be a small pile of rocks, some small pieces of driftwood placed so it forms a protective hiding spot. But even just one piece of driftwood on both sides of the tank would be ok, as long as it's wide enough for them to hide behind.
If food is the issue in there.....not sure what you're feeding...but if it's a wafer, break it in half and put the two pieces in two different spots for them. That should keep them both happy. I'm just tending to think that not enough food is the issue and they are hungry. Real fighting occurs between two males over a female to spawn with. Then it is usually a death fight. I have two males and 6 or 7 females in a heavily planted 75G and I have no fighting. This tank gets fed twice a day though since there are so many of them.