Had the same thing happen last summer, while they were still nursing their mother. Friday they were fine Monday one bout dead and several very weak. Black stools, I made some albon and started them on it and bought some NEW wormer (Pyrantel) and gave each pup 1cc ( I think my wormer that I had may have lost its strength)and then 5 days later wormed them again.. I gave them albon for 7 days as well... they got better.. did loose 2 of them before meds could work. I worm my pups weekly from 1 week of age til 12 weeks with Pyrantel and then give them a stronger wormer monthly.

Fought the same thing last year. Give them 3 cc of albon a piece every day for 10 days. Go to the vet and get albendazole wormer. The albendazole wormer I got from my vet last year said 1cc per 25lbs. So 1cc is definitely plenty. Give it for 5 to 7 days in a row. This turned mine around. You got to worm them more than normal because of how bad hooks can get.

Throw wormer away get some more or different. Had same happen couple yrs ago and bought new wormer, dogs looked find all of sudden same thing happen. Got bad batch of wormer. Got another bottle same kind wormed pups and they started passing a lot of worms. Saved other 3 pups lost 2.

Yea the hooks have become resistant to the pyrantel. You have to use liquid sa***aurd or panacur(same thing). 2 1/4 cc per 10 lbs is the dosage. A little extra wont hurt in a serious situation as yours.