How is that cruel? You can let them with the parents thats not an issue. Your saying you want to sell them so its best you can them separated. The parents will eat a few or all of them especially if its their first batch and they do this in preparation for the next batch.
Breeders have been taking out fry for decades from their parents. Sorry to say but convicts don't fetch a lot of money. I had fry before no LFS would take them for a monetary amount.
Good luck! Its okay keep them with the parents but don't be upset if they end up eating the fry which is very common to do.
