Is there a "neutral" territory where you can introduce them to each other without the territorial issues of introducing them on the older dogs turf? Maybe take them to a nearby park, get them used to each other, take them home in the car, and let them loose at the same time in the house. Watch for mealtime aggression or fighting over sleeping or other space for a few days. Make sure the puppy is yours, not the older dogs. By that, I mean the older dog should not be allowed to act superior to the puppy - they should both be equally submissive, and thus equally controlled, by you. If the older dog thinks he can dominate the younger dog without you doing anything about it, he may start to think he has a chance to climb even higher in the pack, which isn't a good thing.