
Try not to expect too much too soon. The bitch and his siblings will certainly have started the lessons on bite inhibition - but it will still need several more months of persistent reinforcement for it to be properly learned. He also has his teething to go through yet, when a lot of chewing takes place.
At 12 weeks he is too young for 'exercise' as such. When did he have his second injection and was allowed out in the street? As a general rule of thumb a pup should have 5 minutes walk for every month of age - so your 12 week pup should have walks of no more than 15 minutes each. These are not 'for exercise', but more for training and socialisation - he will get enough physical exercise around your house and garden.
Don't forget that mental exercise (training) is as tiring for a pup as physical games - and he is by no means too young to learn basic obedience. Do you take him to training classes?