Are they fighting or are they playing roughly? If one runs, hides and avoids the other then it might be fighting. Or if they are both provoking each other trying to be dominant, it might be fighting. But if they always come back for more that it is probably rough play. When Biddy plays with Kim is sounds like fighting. But she does not fear him or provoke him . She just tells him loudly that he plays rough.
Are the sessions short, or constant? Another clue. Playing will be short bursts of fight sound and then off to do something else. A real fight may continue for a long time, especially if one does not back down.
If you really hate it, squirt them with water to break them up.