As to the 2 incher. If you have ever had peacock fry you'd see that at least one male colors early. Just ask RustyNut about the beautiful male peacock I sent him. That guy was maybe over 2" and had lots of color. His sibs weren't showing anywhere near the color but I can still pick out potiential males based on seeing some color early. It's actually much harder to pick out females as they could be sub-dom males that won't color up until the dom male is gone. Once I removed the dom male from the group of fry/juvies, now other males are coloring up that wouldn't with the dom male around. It's just how peacocks are. IF you find a whole tank full of colorful male peacocks at 2" THEN suspect hormones.
As for the 3" peacock. It's possible he's male but not dominate enough to show his color yet. The dorsal stripe seems to exist in females but they get it at an older age. Signs I look for in my lemon jakes include the dorsal stripe, fin color changes, and yellow hood (since they have yellow) long before the blue begins to show up in the face. Hopefully that helps you out.
C. Afra "cobue", Labidochromis chisumulae, M. joanjohnsonae,
Ps. acei, Ps.cyaneorhabdos, I. spengerae
46 Bow front
Ps. saulosi, Labidochromis chisumulae