Sounds like your pup is trying to move up in the pecking order of the house. You MUST put a stop to any and all undesirable behavior. I don't even let my dogs growl at each other inside the house. And they all have the fear of god in them when it comes to me. I do not beat them, but I did use a spanker when they were puppies. Just a rolled up ad to swat at them when training. You never want to hit them with your hand as you don't want them afraid of your hand or anyone elses. That might lead to biting someone. Now if they misbehave a simple "NO" or "Ah Ah" from me and they stop whatever they are doing. Use a firm voice when issuing commands to. Different from your playtime voice so they understand. Dogs pick up on tonal changes in our voices.
Now my husky was a bit of a challenge. Similar to German Shepherds they are high strung. I had to physically pick her up by her jowls and stare her in the eyes at the instruction of a Husky specialist through the rescue I got her from. So all 4 paws are off the ground and she is helpless. Then later on when she did challenge me once or twice, she was on her back with me screaming in her face before she realized what hit her. Like I said, you nip it as soon as it happens. I can say it does work and all of my dogs are well behaved and have never nipped anyone, whether walking or at home.
Dogs have a few unique things they do that people don't realize. The major one I picked up on was when they come and sit looking at you and then place their paw on your hand. While you may think this is cute, it is actually a sign of dominance. They are trying to exert their dominance over you. So you put your hand over their paw or swat their paw off. I have to tell any visitors to my house to not let my dogs do that. They always try but get the hint pretty quickly. Most people do not realize what the dog is doing when they do that.
Good luck and just stick with it. You gotta be consistent when training a dog. You, your wife, and the kids MUST use the same rules, commands, etc. And before you know it, you will have a well behaved dog that knows it's place in the family.