I remember one time when two brothers were arguing, and one of them stretched out his foot, which began to provoke the other, who then slowly became angry. They would kick each other, at first lightly and then with more force. Actually, when you see this kind of situation, you will feel very angry.
First, do not stop them, because when you stop them, you are characterizing one person as wrong, and after you characterize them, one of them may become even angrier. The worst thing is that they may both become angry together and say, “We’re just playing; why are you taking it so seriously?” So calm yourself down first, and then ask them casually, “What’s happening now?” Sometimes they may answer you, which is already good. If they cannot answer and are still angry, you can separate them, which is also okay.