Initially a new member should be kept in a separate room for a few weeks. As dogs and cats produce their own scent which they use for territory marking with urination, it's hard for the older ones to accept the new ones easily. During this separation period, you can switch the bedding on alternate days so that they get used to each other’s scent. Get them toys separately and swap between them. Give them playtime for few hours together under your supervision. Give them feeding and water bowls separately.
During the playtime use treats to praise and introduce them. Use commands. The whole process will take a month or so.
You can prefer GSD or any breed or even Indie, it hardly matters.
My do won’t become full know few of them told when you bring the pup you constantly keep an eye on your pup so the adult dog will become dull I heard of this dr. Is it true