German Shepherd Training

It's not at all unusual or uncommon for one to pick on the other. We had an Anatolian Shepherd male, a Husky/Shepherd mix male, and we added a Shepherd/Husky mix female to the mix. When it was the 2 males, they got along very well, the Anatolian was the elder (he died in Jan 2021), and clearly the leader. We had a female Rotti/Lab mix when we first brought Charlie (the Husky/Shep male) home, and she was fairly passive.
What I noticed when we first brought Olive (the female Shep/Husky) home, was she would try to initiate play with Charlie, who would interact with her, but that Dunham (Anatolian), would quickly step in, and Charlie would step aside. in the past year or so, Charlie has been playing with Olive much more, often initiating the play, where she was always the first one to start before.
Olive has always been much more aggressive towards Charlie, always biting at his legs and ears, though she very rarely hurts him, and he generally doesn't retaliate. She is much faster than he is, literally runs circles around him, but they get along extremely well. As for training your GSD, I always prefer a gentler approach, using positive rewards like treats and food as a motivation.
Charlie was about 9 months old when we got him, and had absolutely ZERO training, he was about 45 pounds, but he was capable of dragging me around on his leash. (I'm 6'7", around 290 pounds) He also has a wanderlust, and will take off on his own if an opportunity presents, though he has gotten better in the 7 plus years we've had him, but I still don't trust him enough to allow him off the leash anywhere but an off-leash park or a fenced yard.
Patience is the key IMO, learning what your dog responds best to will pay dividends in training. I have used food with great success, in training several of my dogs, and kindness.
At the end of the day, sometimes dogs simply have to establish for themselves which is the leader, and all you can do is ensure that they do not hurt each other. Neutering will go a very long way in this regard as testosterone triggers more aggressive behavior in any animal than anything else.

Good luck with your pups, they are great companions that provide unconditional love and ask very little in return.