If theu lose more than 10% of their body weight you need to do something. I would try supplemental feedings of the babies but don't stop them from nursing totally! Are you giving the mom a calcium tab every day? I would get them to the Vet.
By the way, my Kalina never EVER had obvious milk - it never dripped, I could never squeeze any out of the nipple; but her puppies were obviously getting plenty because they were FAT and gaining every day. And, yes, being OCD I weighed them every single day. But yours are losing weight, so you need to do something right away IMHO.
Good luck and let us know what the Vet says.
