Grinding flakes is an option, a bad option to mine opinion but an option.
Better than nothing, but they can't eat most of the flakes because it is to big.
Go out and buy something like: Tetra Cichlid Shrimp Sticks.
Use a unused salt mill and put there the sticks in.
Now you get powder food which wil fit in their mouth.
It is wonder-powder for me guppies, won't expect anything else with mollies.