If the owner said they were feeding live chances are thats what they will prefer to eat. You can go to live to frozen but it takes time, versus frozen to live which I think is supposed to be a lot easier. And seeing as how you just got em and its only been three weeks just give it some time. When I got my girl she didnt eat for a few weeks, then she shed and took a mouse as soon as I plopped it in with her. Just keep em with the right temps, humidity, and feeling "secure".