One of the heartbreaks of being a dog rescuer is that none of us can save them all. It's just not possible. Hard choices are part of the burden we have to bear in order to save the lives that we can. We voluntarily accept that burden, because every life we save matters.
For the dog that gets picked, it means everything.
Do you best to make your decision as objectively as you can, not based on the emotion of the choice, but based on the best dog for you to live with. Tonight, try to make a list of all the specific qualities your perfect dog would have. Take that list with you to the shelter, and mark off which ones each dog has, so that you can compare.
Make your choice based on real criteria that are important to you. For example: which one would be easiest to train, to introduce to your dogs, to live in your home?
You can't know if the ones you don't choose will be euthanized. You can, however, network them -- on Facebook (German Shepherd Community), here in the Urgent section of the forum, and elsewhere to help get the word about for the dogs you have to leave behind. There may be another family that comes to get them -- or a spot may open up in rescue on the last day. It's very, very common for rescues to wait until the last day to pull dogs -- they sometimes swoop in and save a dog hours before its scheduled euthanasia. That could very well happen for any of these dogs -- they are all beautiful, attractive, young, highly adoptable dogs.