Ever see Strawberry Rasboras ? Tiny fish, not even an inch full grown. They are schoolers, so they don't do well alone, but even in a tank that size you could have five or so, if you kept an eye on the water and did lots of plants. Very cute, and while it would be best to have one male and the rest female, the males are not especially territorial. Sexing is not too hard, the boys have a much larger black blotch on their sides compared to the blotch on the girls. Super cute little guys, colourful too.
Badis, or dario, are lovely, but they are very shy and can be hard to feed. They may not eat unless you provide live food. They prefer to hide most of the time, and if you don't give them hiding places they'll be very stressed and not live long. And one male to one female may mean that female gets harassed. They are better with two or three females per male which is too many for that size tank. Full grown they are close to two inches long. And having two males is no good either, they'll fight each other, they are very territorial.