Hi. I was hoping to get a response back before giving you an answer but I feel this is important enough to supply you an answer based on the information already given.
There are many reasons your puppies may be failing that include serious worm infestation, flea infestation causing anemia, herpes virus, and bad milk from mom or congenital health issues. It is sometimes referred to as fading puppy syndrome.
This site has information on fading puppy syndrome.
Based on your description, I fear herpes may be an issue. Herpes can cause yellow green feces, a lack of appetite, weakness to only name a couple symptoms. You can read about herpes here:
This site goes over ways of helping save fading puppies.
I strongly suggest you start trying to prevent dehydration and hypoglycemia by administering small amount of formula with a small needleless syringe regularly and putting a drop of pancake syrup on the pups gums. If you put a little syrup on mom's nipple, the pup may suckle and get a little milk in that manner. Additionally, I would have the pups and mom seen as soon as possible by your vet so they can test for potential parasites, protozoan infections and help rule out herpes as the cause. Protozoan infections can lead to yellowish smelly feces and a loss of appetite as well.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.