
Can you take a sample to get it checked out that there is nothing nasty going on, doesn't matter who the sample came from if they are all having the same problem.
Could Mum have picked up and eaten something outside that has gone through the pups, could have been something as simple as chewing grass.
I would be surprised if the vet gave antibiotics without an obvious infection as they are more likely to mess up the good bugs in the bowel. Worming would be my first thing to do and see how things go from there and check for any worms, don't forget Mum too.
Check the pups are not dehydrated, pinch their skin and it should spring back, if it takes a while or stays in a peak then they will need sub cut fluids to tide them over. Has Mum got plenty of milk to keep them well hydrated through this hiccup?
Hope things are sorted soon