New dog added to the home, and one gone! Frightening aggression!

Hi! I have a 2 yr old male velcro...I mean Vizsla. Sweetest tempered animal I've ever seen. My ex-roomate and his female vizsla just moved out and my sister and her feist (1 yr old squirrel dog) just moved in. Immediatly the little feist began showing signs of aggression (barking, nipping and circling), while Barron, the Vizsla just seemed to be taken aback. He rises very tall and stands his ground (hair mildly raised) but doesnt move. I am scared that if he does react it could be bad. I scold the feist and remove them from each other, but I just feel like I am delaying the inevitable. How can I sociallize them better and not provoke a fight? Any Vizsla owners know just how sweet they are...I dont want to instill fighting in him and dont want either dog getting hurt....HELP!!!!