Is it possible for all the son of a bald man to not go bald?

Yes: Both graying and baldness are mostly genetic- ask your older relatives when they lost their hair or started graying. Sometimes, medical illness or certain stressors or medical treatments(like chemo) can also cause hair loss or gray/discolored hair. Male pattern baldness is carried by the females- so it is possible to have a bald father and sons with full heads of hair.