I think I am more concerned about adding two who are bonded to my labby who was here first....how would I add these two without making my guy feel slighted?
I think your older dog would adjust just fine. Think of all of the running he will do with friends to play with. You might feel slighted because he might not play with you as much anymore.
We have made it a point to separate our two every once in a while for a little one on one time (puppy needs undistracted training time, schnauzer needs ears scratched without puppy chewing on his face).