A good book and subject to study is any thing related to good etiquette for children (and marriage too).
A start may be to read works by Emily Post. “The Gift of Good Manners” by peggy post and cindy post senning are pretty good reads.
The writing is well laid out. However, you must use your own discernment through scriptures to help you interpret how to relate to improperly arranged marriages and out of wed-lock relationships. However, having the WISDOM of how to keep ones lips closed can go a long way to victory in any relationship.
Good manners will help you deal with un-rulely and downright rude in-laws. If you have the ability to outshine them, you will rule the coop and they will not have the ability to take control of you or your kids.
Giving your children the gift of good manners will help them in SO MANY human interactions.