Abusive people act the way they do in order to upset and depress others. They live and thrive on people's negative responses and reactions. If you meet their abuse and rudeness with a smile, you never defend yourself when they accuse you of anything, even if little and you don't argue with them at all, this would kill them slowly. Whenever they talk trash to you, simply smile and do not respond or engage with them, as if they don't exist. They will shout and scream, but you will remain calm and show no reaction to whatever they say or do. After some time, they will feel silly and neglected and they will eventually stop. 

Abusive inlaws

Kindly refer to the following link(s):

How to deal with Abusive People? 

How to deal with rude and arrogant relatives (Kith and Kin)

How to deal with ill-mannered people? 

Abusive Mother in Law  

How to not lose your cool & deal with people who insult you in your face?