NeonFlux,
You definitely do not have turquoise rainbows. The last picture you showed is of two FEMALE boesemanis, I think the other one you have is a female incisus, but hard to tell because she looks pretty young and is very pale. You also do not have affinis, arfakensis, misoolensis, monticloa, or synergos, you would never find them in a lfs, they're far too rare. I'd return the incisus and try to find a couple of male boesemanis and probably another female, the males are easy to type because their front half is blue and their back half is orange or yellow. Rainbows do best in a school of five or more. What are the exact dimensions of your tank? If it is a really tall tank, you might want to add some extra aeration as rainbows are oxygen intensive fish.
Catfish69hunter, how long have you had the turquoise? These fish really do get bigger than 3 inches, they should grow to at least 4 inches and some might even reach 6 if given the right environment, but they grow very slowly and in a tank as small as a 28 gallon, yours might be too restricted by the tank to reach his/her full potential. My turquoise is currently 4 inches and still growing.
A couple final notes: Just because G. incisus are from another genus does not mean that they won't interbreed with M. boesemanis or M. lacustris, on the contrary, both of these crosses have been documented, and will result in viable fish, but they don't look nearly as nice as the pure species. Also, the incisus, boesemani, turqoise, and neon rainbowfish are all from New Guinea, not Australia.