Where are you getting the turkey mince from? Is it for human consumption, or pet mince from a pet shop?
The reason I'm asking is that 'human' mince won't have any bone in, so will be deficient in calcium. If they're not eating the dry ferret food, and not suckling much from mum, they'll not be getting enough calcium, and you could end up with weak bones/walking problems.
Not a good idea to feed lots of muscle meat alone. Have you tried softening the dry food with a little warm water? If it's soft they should eat it fine. Perhaps two bowls of dried food, one dry for mum, and the ot