Hm, I don't want to sound pesimistic, but rats don't usually stop eating like that. They may slow down with their feedings but , will still eat. Are you sure they are not eating even a little bit? My extra fat long evans rats don't eat much altough they are extremely fat
Have them seen by a vet if they are pets, if they are feeders/breeders and is not practical with the vet bill, you know what's the next best thing.
I hope they get well