I need to interfere or they will get into a fight.

我必须去劝劝了，不然他们得打起来。

For example, your family member asks you What should we do about Syrian refugees? and you don't really want to get into a fight.

比如，家人问你；“我们该怎么应对叙利亚难民？”你真的不想引起争执的话。