You as mommy need to intervene with his behaviors. When he's getting to rough make a loud noise and separate them. Stay on it!!! We just added Milo and he is so sweet and loving and Chloe seems to like to bully him. She is so jealous. When any of my other pups come into the room she goes into attack mode. I pick her up and tell her no and then make her sniff their butt. I saw this on the Dog Whisperer and it does help. She is starting to get it.
Hope this helps!