Plecs create a lot of poo. Two Plecs in a 10 IMP gallon with Corys and mollys would seem to me to need frequent water changes for the Cory and some aggressive filtration for the Plecs. I missed actually how the tank is already stocked.
Corys feed by feeling around in the substrate with their barbells. I have watched worms escape them easily. I doubt they would go after your midlevel and top level fry. It would seem like it would be more unintentional. I have a pair of guppys breeding in a 29 USG with harlequin Rasaboras, Jari zebra Plecs (an omnivore) and a large number of Corys. I have not seen any swimming after the fry for a snak. I have to soon start finding a new situation for the fry as they are multiplying without any help.