Hi Maya. What a lovely puppy, he looks so cute.
Your problem is a very urgent matter seeing as u have children, but unfortunately it isn't as simple as throwing out a quick answer as there seems to be under-lying factors that i suspect you have not mentioned. For him to be chewing and nipping you he obviously does not see you as the alpha, which is very important that he does. By nature he is not a dominant breed and would love nothing more than to take the follower position as apposed to the position he holds at the moment.
Firstly, the 2 key factors to controlling an un-stable dogs behavior is consistency and timing, n that goes for any un-wanted behavior trait imaginable. If you were not consistent and timely with your corrections when he first started nipping and chewing, that is probably why he still continues that behavior.
It is imperative that you have the correct energy around your dog and the walking and lead chewing issue may be as simple as how you project your energy on walks....in other words, if you don't enjoy walking him and get frustrated when you have to go on walks, he will pick up on that weak energy and that will cause him to react with un-stable behavior, i.e the dominant lead chewing and growling.
He must be calm before he leaves the house for walks, and more importantly, u must be in a positive frame of mind (think of happy times and re-play them in your head as this will make u have a good energy).
If before you walk him u start to think things such as "how annoying this walk is gonna be", or "damn, another walk with hell hound here, i wonder if he'll chew his lead n be a naughty little shite", then you are building up a negative energy. Tell yourself that this walk is gonna be a new start and that you have everything under control, but MEAN IT because he can tell if you are just PRETENDING to be in control.
You have to be relaxed when you are holding his lead because if ur tense he will pick up ur tension and take over your weakness with dominance. Timing is of paramount importance so as soon as he starts to go for his lead, give his lead a sharp tug to the side and it will snap him out of the next move he was about to make, which will have been to grab the lead in his mouth (don't tug the lead back as this only heightens the tension). A good example of this is when somebody taps you on the shoulder from behind and you immediately turn to see who it is and it re-directs ur attention away from whatever you were focusing on before hand....this is the behavior you want to create, if you take his attention away at the right time it will prevent him from escalating to the next level of that particular behavior.
As soon as you have corrected him (lead tug) relax the lead again and carry on walking. Repeat this as many times as you need to for it to become the norm on walks, like i said, consistency is one of the 2 key factors. If he gets past level 1 behavior quicker than you can snap him out of it, stay calm, don't get frustrated, stop, and assertively put him in a sit position until he becomes calm again, then when he is calm, YOU begin the walk, don't let him walk off first. Remember, you are in control. Remember, don't anticipate his bad behavior as that will only make him react how you are thinking he is gonna react.
I have chose to advise you on the walk first Maya as this should be the first step in becoming a respected an authoritative pack leader. In the dog world it simulates the hunt as in, u leading the walks is like the alpha Wolf leading the pack on a hunt. Get the walking thing locked down n you inadvertently curb other behavior issues.
As far as the nipping and chewing of fingers n hands is concerned, bite him back! Thats right, u read this correctly, i said bite him back.
Not with your mouth but with your hand. Ive used this hundreds of times on dogs who ignore most corrections, most recently on a friends American Bulldog who was a serial nipper.
Your dog isn't playing when he does this, he's being down right disrespectful. Please bear in mind that I'm only advising you to bite as you have already said that you have tried numerous ways to get him to stop, and he obviously is not taking you serious. He needs to know that you MEAN IT when you correct him so before i advise on how to do this, let me tell you about the bite.
The alphas and omegas in the wolf pack use the bite on the sub-ordinates as a method of assertiveness and correction. They will assertively mouth the head, face or neck and apply a medium amount of pressure to let the other wolf know they mean business when persistent pack members test there patience or behave un-desireably.
So, to do this effectively, create a letter C shape with your hand to simulate the shape of a mouth and without being tense, prod it to the neck area. This should ONLY be done if all else fails, it is not a method to be used in every day behavior. Stay assertive when you apply the bite otherwise he will look at you and think "are you having a laugh love, what was that? a feather duster, n u expect me to listen to you? get real"
You must be calm and be assertive when you apply the bite, and after you apply it. Trust me, if you get the timing right, he will wonder what the heck has gotten into you and he WILL take notice.
Lets look at a correct scenario
You are siting there minding your own business and Mr Nippy comes to chew on you a bit.
Maya: No! (use an assertive tone but don't shout as this projects frustrated energy)
Mr Nippy: (ignores the No correction and carries on nipping away)
Maya: (apply the bite to the neck just above the shoulder blade)
Mr Nippy: "Uh Oh, she means business"
If he continues, which he shouldn't, then repeat until you have the desired affect. You will definetly not need to sit there repeating this correction if you get it right the first time and the second time if need be.
By now you probably need laser eye treatment after reading my version of War & Peace, but i cannot simplify my advice for the sake of easy reading, its that important!!!
I really really hope you get this sorted and i hope you let me know how its all going. I'm sure ur successful in raising your children n that they see you as a figure of authority, so applying the same assertiveness with your dog as you do with your kids may help. Remember!!!!, assertiveness is never aggression, frustration or anger, and you don't have to be physical to be dominant!
Dave