Your pup hasnt been weaned properly i.e the age when a pup should be separated from his mom;the right age being atleast 8 weeks, so ur Puppy Businessman is to be blamed. He hasnt socialised properly with his siblings too since u got him early n its normal for him to miss them.You have to be patient, it will get better with time.He will be Ok in another 4-5 months but will be a problem if u get angry, scold him or even hit him. Be patient.
40 Day pups dont respond to names, wil, take another 4-5 months, but only if u treat him lovingly.
You should never leash him at such a young age, it has adverse effects on their neck, backbones and entire structure.
You can engage him by letting him play off leash only. The bonding starts now so treat him nicely.
A simple calculation is to multiply dog age * 6 so would a human baby respond to names at 6 moths..no..but they will respond to love , affection and fun during playtimes.
They do tend to bite and nibble into things at this age.Its normal, dont over react or get angry. He is just a baby.