I would get him to a dog park for some quality time with other dogs, and exercise. We have a special side of our park that is only for small dogs, it's great because I don't have to worry about a big dog grabbing or trampling my babies.
In my opinion, tired puppies are happy, well-behaved puppies, and 2 walks a day just isn't getting him enough exercise. You might also consider doggy daycare a few days a week.
Regardless, getting into a training class with a good trainer will do you tremendous good. They will work with you on getting him to focus on you, on helping you communicate with him, and getting him to understand what's expected. It is money well spent, just make sure you have a good trainer, certifications are usually APDT, and CPDT.
I would definitely not be growling at him.
Agree with this -- issue is probably in part that just a walk is not too much activity/interactio -- not like daily at home training, a kong toy to keep him busy, and so on. Thinking is harder than playing and an important complement to walks. He is shy at classes because he isn;t getting enough interaction with other dogs/people except the ones at home and is working out all his energy there. Lack of socialisation can cause difficulties including fear aggression and frustratingly -- more barking -- so really important to get him into class with a good trainer who knows classes are about more than getting a dog to sit/down etc -- and make sure he gets regular socialising with other pups/dogs of different sizes, in safe environments.
Please, please, also try as best you can to not go off on the very wrong, long disproven track of labelling *absolutely normal puppy behaviour*
as 'dominance'
-- this is not dominance (and dominance is so badly understood -- it really has nothing at all to do with what we assume is 'dominance' and should be thrown out of popular training vocabulary -- more dogs have been seriously managed due to people using problematical and damaging 'dominance' training tha probably any other single approach to dogs -- it routinely causes fear aggression. See my links pinned in the training section on this.
Also anything written by Dr Ian Dunbar on this -- just google his name and 'dominance').
Have your training classes taken the dominance approach? Have you talked to the trainer about the 'at home' issue? A good trainer would not be letting a shy puppy sit on a lap/be held -- he needs socialising/interaction.
Also he is just 6 months old -- you need expectations in line with his age. He's just a young kid in dog terms and also -- getting to the age where hormones kick in and he will be even more distracted. Neutering when he is slightly older will help but you do have some things to consider longer term as noted below.
Basically you have a lively active *normal* puppy and he plays with your older dog in an absolutely normal way (older dogs often play in this relaxed way and do not want to 'stick up for themselves' -- but if Charlie is endlessly under pressure just separate them and let him have some quiet time
). BTW around 6 months, pups lose what Ian Dunbar calls their 'puppy license' and older dogs will do the job of scolding too rowdy behaviour IF they feel it is warranted -- just let them alone in such cases, it helps a puppy much better to learn from other dogs than intervening humans who do not speak 'canine'!). The pup just has not had enough training to know what to do -- he needs daily fun constructive practice
, and he should never have to be afraid /fear you! That isn't the basis of a good relationship at all or good training
). instead he probably needs more activity. And some puppies are just more vocal than others!
On a serious note that you will have to keep in mind: This may end up being a issue for you if people are complaining -- it really can be virtually impossible to train a barker not to bark, especially when you are not there. Punishment will NOT help this situation. Also if you have a really active dog that you are not sure you can manage due to health issues or just generally (he sounds like he may well have a far more demanding personality than Charlie -- I have one like this and this will NOT change. Such dogs need activities like agility/tracking/daily dog games etc or get very frustrated)... to be honest it may mean this is a dog that needs a different home, as difficult as that is to think about. And dogs bark -- some more, some less. It is how they communicate. Just like some kids are noisy, some are quiet children. Did you talk to the breeder about wanting a quiet low key puppy? Good breeders can help owners get the pup most likely to fit the bill -- the active friendly puppy 'that chose me' is typically the worst choice for people who want a quieter dog as the lively one is going to be the most active and pushy and most in need of lots of exercise, interaction and busy-work!
In summary: there are some things you can definitely work on, and some that are probably his personality, more exuberant, lively, active and barky than your current dog. Outcome depends on how much focused time he gets from owners, and also how much commitment there is to work with a dog of this personality, which is likely going to be more challenging to you full stop (and if neighbours have complained than your options may be limited to rehoming or moving).
But FIRST: I would follow the quoted advice above. Get into a training class with an APDT or CPDT trainer in the UK (the association websites list local trainers in US and UK). And download Ian Dunbar's FREE book After You Get Your Puppy to feel more confident about managing your pup and learn more about normal behaviour and how to train:
www.dogstardaily.com/free-downloads. If you have a trainer that tells you you need to 'demote' your puppy, that he is 'dominant', etc then get a different trainer.