I'm having the same exact problem, my female has only breed once and even though the female and the male are constantly flaring their gills and digging up the gravel they will not spawn. I guess they just don't feel safe
those small babies you have are straight up mercenaries. ive found the best predator to wipe out fry are small cons. i once watch a male of mine w fry try to move his fry from 1 spot to another and 3 smaller cons formed a triangle around the old spot n new spot. he would move a mouthful to a new spot and when he left, 1 of the cons would distract him and another would go eat up the fry in the new spot. so he kept doing that over and over until the 3 smaller cons wiped out all the fry. pretty cool to watch
remove the fry from the parents they will not continually breed if they are raising broods. if you remove the fry at 2 weeks - 1 month in age the parents will surely breed soon after .
I like the looks of convicts however when they breed if I don't have anything to feed the fry to, I end up with way too many that are hard to give away! I really wish I had the problem of convicts not spawning!
My cons breed like I'm gonna sell them the next day. I let them raise the fry for two weeks then I separate them. After two more weeks I would have eggs again. My cons are in a community tank and the fry usually end up being food for my other fish.