If you're going to introduce a strange dog into your house, it will probably be less stressful for all the dogs to have their first meeting at a neutral place. Like a park. And when/if the older dogs start growling at the pup, remember that is normal for a pack. Everyone will know there place within it in a few days. Growling and posturing is normal for strange dogs. But anything beyond that should be nipped iin the bud. Make sure you don't fuss over the pup in front of your own dogs. Don't shove your dogs out the door and let the pup stay in if things get hairy. A "time out" with a stern look should do it.
Here's a photo of my GSD Jack. I hope it comes out! If not,try try again.