Wow, he is *really* young! As you've already realized, they are extremely vulnerable at this age/weight - so it's good that you're so on top of everything. Most yorkies are not allowed to leave their Mom until 12-16 weeks of age - so this is another sign of what that breeder is about
. I'm sorry your going through all of this.
My Marcel hated that A/D - so although it's full of fat, it may not actually be that appetizing. Marcel also choked on it and stopped breathing bc it was SO thick. At this point, you really just want to get food in him. I'd probably go to a good pet food store and get some premium canned puppy food (perhaps a few brands) and see if you can find one he likes. Baby food is an option, but not long term as it's not balanced for dogs and can actually then make them sicker. Marcel really liked those toddler hot dogs (in the glass jars) - so try that.
I agree w/ Crystal though - you may need to do bile acids on this baby. But, there is also the likelihood that he is just very sick and exhausted - he was probably sick for awhile (and untreated) at the breeders. So, he could just be trying to recover - which is difficult when he's not eating. I would also give Nutrical (which has a lot of vitamins) about 4x per day at this point. Flavor his water w/ Karo or Honey to get him to drink.