I have never had Mainganos, have had the other 2 species. I wouid wait til you get Mainganos that are about the same size, but of course by then the Socolofis may have the tank dominated. What size tank do you have? For these 3 species I would say you need at lease a 55gal, a 75 would be better.
I could put the labs in the 75 right away, then put the socolofi in my 28 gallon bowfront till they are 2-3 inches, then add the 2-3 inch maingano to the tank and then add the socolofi in shortly after
but I was thinking it would be good to have them all be close to the same size