I have 3 male Siberian Husky dogs. One is the father, one is the uncle and the last one is the son. Anyways, the father and son fight and sometimes the uncle and nephew fight. It could be over attention or over treats. How does one deal with this? When I just had the two brothers - they never fought - then the son comes along and they growl at each other. What does one do?
Sometimes dogs have influence over their "playmates" or "family members" which can be positive or negative. The newest addition to your pets seems to have this issue. I would suggest taking time alone with the one dog, playing with him, feeding him treats, etc.