We have 3 dogs in our house and a friend is moving in with their dog. Our oldest dog and the youngest dog keep trying to pick fights with our friend's dog. How can we prevent this?

We have 3 dogs in our house and a friend is moving in with their dog. Our oldest dog and the youngest dog (golden retriever and chihuahua) keep trying to pick fights with our friend's dog. How can we prevent this? My mom tries punishing them, but I know that there is a better way.