How do I resolve problems in between my father and mother ?

We are having this family issue from the last 8-9 years which was firstly within the limits and now it has taken a shape of wide issue that my father has sent my mom's brothers,sister and her son that they do gossip about him to his wife and his son and daughters so that they stop behaving badly with him which is totally wrong. There's nothing like that. He is taking steps on his own persistence. What should i do to stop him for torturing the innocents.