Neutering probably will help, but that's just a definite personality thing. Every dog is different. Bruiser sounds like he's just going to be more upkeep and work than Rocky
Also, he's not being
aggressive by what you describe... he's a 16 week old pup and I've never seen a puppy actually be aggressive. I think sometimes people throw the word aggressive around when it's really just rambunctiousness, fear, dominance or something else. It's all part of their play but Bruiser just seems to be more of a dominant personality than Rocky. Were they younger than 12 weeks old when you got them? Sometimes pups that are taken too young from their mothers don't learn proper ways to play and miss out on learning about bite inhibition. If you were to take Bruiser around an adult dog, they would teach them the ropes! Adult dogs won't put up with that puppy stuff and teach other pups how to be social and respectable to other dogs by nipping at them, etc.
I would suggest exercise, exercise and more exercise! A tired dog is a happy dog, in my opinion!
Wear Bruiser out!! Take him for long walks, have fun games of fetch and tug, and keep up with the training you're already doing
If you channel all of his crazy energy into something good, he could be a real smart doggie one day
He sounds he already is!
Good luck, welcome to YT, hope you stick around! You can learn some great things!