You will need 2 males and 5 females to really be effective. If there is no competition it will be harder to get them to breed. Usually, once they start they won't stop.
Pink convicts are NOT a trash fish. I don't know why you would even think that. The biggest problem about them is that they are essentially the most maniacal killer you can get in a 4.5 in. fish. In spite of their small size, they can and will take on fish 4 times their own size. Due to their aggressive nature and no other reason make them a very hard fish to sell. By contrast, the black (zebra) convict will warn off other fish or attempt to and then only resort to small bites. The pink con prefer to kill. They will even kill their mate if the female is not ready or refuses to breed.
Please take time to learn about any fish you wish to breed and don't limit yourself to rumors and uneducated information.