The most common cause of what you are seeing is a parasite problem, giardia or coccidia. In puppies this age, you do see it a lot. Your vet can check for this with a fecal float.
If the diarrhea is bloody, I would be very worried that they are suffering from parvo.
At this point, they have gone too long without eating. You need to go ahead and give the vet a call and see if they want you to bring them in today. They may need sub-q fluids.
At the very least, you need to rehydrate them using some plain pedialyte. You can also boil some chicken and white rice and see if they will eat this.
But, if not, a vet visit will be necessary.
Let me know if you want to discuss this more.