those oscars have trained you well, lol. they've realized that the chicken livers, nightcrawlers, and brine shrimp taste better than pellets and other prepared foods.
fast them for a few days (as long as all fish in your tank are in good condition and good health) and then try pellets again soaked in garlic juice. should solve the problem. save the yummier foods for occasional feeding so they don't get into the same habits again.
flake, IMO, isn't the best option for larger oscars. they'll make a big mess with it, chuffing it out their gills and not getting much out of the food. at least i know this with my oscar, Gus.
also sounds like your tank is pretty overstocked. i'd look at moving some fish to another tank or re-homing them if you don't have other tank space available. a 135 gallon is a good size for 2 oscars, 3 if they are not full size yet and get along well.