I usually have best luck feeding exactly the same way the breeder was feeding, before switching to something else. For example - if they were feeding mice hoppers, I feed mice for a few feedings while they get settled in. If they were on live rat pups, I would feed live rat pups.
Are you trying dead rat pups and dangling in front? If so - I would try a live rat pup. Sometimes hatchlings are finicky and the "right" temp and behavior of a live rodent will do the trick. Also - if they haven't been eating rats, try a live hopper or small adult mouse. Mice have a different scent than rats and can often help. You can convert over to rats or frozen/thawed later, once they are regularly eating in their new home.