For Piplup, you can find the "Rare Candy" in the area that you had followed Bennett to (Beryl Wall I believe).There should be two paths, where the right path has a rock which you need to click on in order to get it.
For Eevee, you need to be in the area during a windy night. Once that occurs, the tree should disappear and lead you to the Mysidia Cove. Inside the cove, you'll notice rail tracks bent and pointed in certain directions. I believe you just need to go in the direction that rails aren't pointed to.
If you need more clarification, do ask.