It certainly sounds like they're in the process of pairing up, and spawning shouldn't be too far away. When mine first spawned, both male and female were pretty much the same size (2-2.5"). Now, the male is about 25% larger than the female.
Alright thats good! Also what I noticed about those two is that their tails are really yellow!! The other three are not really yellow at all and they have more black blothyness (i don't know how to describe it) body like the pic you posted while all others are a very consistent beige with a tint of blue!