Thats really weird that your Cons still havent produced...mine will breed in a well stocked tank, an emty tank, hell they would prob go at it in the kitchen sink lol...
I would for sure take out all but one female(the largest is your best bet but not required) and just leave them be for about a week or so and let them get good and settled and soon you will wish you hadnt started breeding them because you will have more than your fish will eat lol
What temp do you have the water? Mine prefer as close to 80 as you can get.
temp is 80-82, and no trust me my fish will be able to easily eat them all before they get outta control lol... oscars, peacock bass, arowana, etc etc