Is it okay to handfeed a newborn puppy with a formula while nursing with their mom?

My dog has only four pups but her milk easily run out because she doesnt eat much, so is it okay or should i stick to one?

You should call a vet and ask.

Please call your breed mentor with your questions, the person you got to know while showing her to her breed championship/working titles. There are also the vets who did the health and genetic testing, prior to breeding. There is the vet who did the ultrasound and prenatal care. There is the vet, who within 24-72 hours, did the wellness checks, and who removed dewclaws. There are the members of the breed club that you belong too, as well. With all these resources at your fingertips, you don't need to ask here.

It's ok for them to have the puppy formula at the same time but you want them to get as much milk from the mother as possible as they get their first antibodies from it thus making them healthier. If the mom is not eating much try a high quality puppy food with pieces of cooked chicken the smell might make her want to eat it more and the puppy food is high in nutrients beneficial for the pups.