Avoid milk instead give him yogurt, no more salty biscuits give him marie gold instead. Instead of Pedigree, try giving him Science Plan or Taste of Wild. Mostly hairfall/dandruff occurs if the dogs intake more grains/grains mix food. Remember dogs are carnivorous by science not omnivorous, yes they eat whatever we give but this doesnt mean whatever we give suit them.
Also, regarding your another question labs are bred for family dogs and it is no doubt that he welcomes strangers, even my lab does same thing, he welcomes strangers and friendly to everyone. Aggressive labs are outcome of faulty breeding or poor raising. Happy with your lab, and from your question, i see that your lab shows absolute submissive behaviour or he might be scare of family members who scold him. Dont expect agressive dog as having agressive dog is not easy.