Amy K. Imagine these fish in nature and not in an aquarium. They spread out a little and they don't invade and REMAIN in each other's territory. So the same is true in aquariums...given enough room and plenty of food, They don't require tons of space because they are small fish. I find that they just don't bother each other once you find that nice combination of territory size and cover and food. Of course they give each other a once-over when one is new to the tank, but unless they are forced together in some tiny tank, they are not inclined to fight. I'm not trying to encourage fish fights by the way, so I really have no reason to mislead people. I am just suggesting people think of their tank as being a portion of natural environment and spread out your fish accordingly. Don't put 2 males in a 2.5 gallon tank and think they won't fight. God luck.

But they breathe on the top of tank so the bottom one always has to cross territory line...?

not unless you have it planted to an unbelievable level and your individual fish are not especially aggressive. I have multiple males with 9 females but the territory is 125 gallons, 6 feet, and planted.

the females can be aggressive, i would not recommend less than 3, 5 ideally. And there can be some aggression when adding a female but the pecking order will then establish and they will be peaceful.

Shelly Tam no. Females can live together called a sorority.