Sorry to hear about your dubias. I don’t understand why people do this. At least your local pet store took the colony and put it to use though. PetsMart would have no idea what to do with it.
From what the previous owner said, they were all eating live. The largest one was eating rats, but everyone else (including a 900g female?) was on mice. I don’t think she had ever tried f/t. They all seem pretty hungry though so I am going to give f/t a try. Worst case scenario, my local exotics shop sells live feeders, and while I don’t like the idea, I understand a fed snake is better than nothing.