[Amazing Yorkies]

I hope they let you take mom and babies. Maybe you can get him to a Vet. Especially since we don't know if anything is wrong, like a cleft, how tiny he is, or if he's a preemie. If he is, he can't tolerate replacement! A Vet will help you with an exam, and tell you what to feed, when to feed, and how to tube feed. In the meantime;
A heat lamp or a heating pad under several blankets is better than just wrapping him up. If you don't have those, stick him in your bra.
Never feed a cold puppy, it will kill him.
I use Esbilac and I'm sure you don't know how to tube feed (which the Vet will show you), you can feed a drop at a time and make sure he swallows. Feed 1 cc per ounce of pup. Be sure to potty him too. I feed every hour until they are on their feet, because I usually can't drop in a full cc of replacement until they are on their feet.
Don't wait until morning to get replacement. Either go to a 24 hour Walmart or use the recipe I think is listed on a sticky here.
*You might have your Vet schedule a spay before you return her to your relative... or better yet, don't return her! It's really horrifying that they wouldn't go to the Vet! They shouldn't be breeding! Not sure they should own either.
Good Luck, I hope the puppy makes it!