Go with vet B: I can't attest to the medical advice, but the diet advice is correct.
The bread and milk are not good staples for a dogs diet, given on occasion is usually ok depending on the dog.
Get a good dog kibble, you can add fresh veggies if you would like, pulverized for better absorbtion.
I will someone else chime in on the supplements.
As for exercise, nothing forced. Freeplay in large fenced areas where the pup can choose when to rest is best for growing joints. Short walks around the neighborhood and to different areas of town for socializing are best.
Last, get the weight off, excess weight can be detrimental to puppy growth. Puppies should be lean, you should see a defined waist from a bird's eye view, and a side tuck starting at the last rib. A healthy puppy will have small muslces in the front and back as well.