Looks like the one with red on its fins and belly experienced some kind of trauma. Hard to say how serious it is. All you can do is keep water extra clean to avoid complications and hope it heals up.
No insight on sexing, I've never managed to sex my own.
It's not easy. Some people will use the shape and curve of the fins at the front, by the head. The best way to see it, is if they are on the tank glass. With 5 of them you should have both M & F. Now just ask them to arrange themselves on the glass so you can compare their fins.
The males are supposed to have a sharper, angular fin while the female's is more rounded. It's not obvious IMO.
That's interesting, I've seen them in books, never come across those at any of my LFS's ever.
hard to tell, How many fish is this total? is it multiple pictures of 1 bag of 5? Kind of looks like 5 females in that picture with the sponge filter in it. , like FishDin said, fins are a bit pointer in shape on males and males are thinner bodied than females. when they are adjusted and stuck to the glass and near each other you can compare and should be able to tell the difference.