You already know how excited I am about the new addition . Ben is just too perfect to miss the opportunity for incorporating him into your family and your life. As for Mack, I'm thinking he hasn't accepted that you are Top Dog and he doesn't get to be that. Once he learns his place in the pack, he should be just fine and welcome having a buddy. I can't remember if he has been to obedience classes. Maybe the structure of formalized training would help him relate to other dogs in a less dominant manner.

Ben, you are going to have a great day today and every day.
Welcome home!