This is a very good question, especially this time of year when the holidays are coming. That's when most people find themselves in an awkward predicament.
First, it helps a person to understand why the in-law behaves or acts the way they do. For example, some people grow up very privileged and can be critical of those in today's society who are not. Meaning, some in-laws are much older, so they are very opinionated toward the younger generations. Or, some were raised with different values/traditions. Understanding why they act the way they do helps ease the frustration toward them.
Other in-laws are simply intrusive for no rhyme or reason. Married couples must agree with each other. There can't be taking sides of the in-laws.
The most important thing is to work as a family. The in-law should not be involving themselves in to matters within a family unit, unless the advice is solicited. It only leads to problems between couples and frustration when a spouse chooses the in-law's side.
Limit time with the in-laws. (Absence makes the heart grow fonder.)
Don't allow intrusive interruptions to ruin your plans.
Limit phone conversations.
Have boundaries in place to protect your own healthy marriage.
My ex MIL did some extremely mean things to me, and was very intrusive. The last trip to my home, I reserved a hotel for her. She was used to staying at my home for months at a time, forwarding her private calls to my home, treating me like a servant, and she even stole from my home. I even went to marriage counseling to help my ex understand how I was feeling. To no avail, we divorced anyway. He was not supportive and put his mother first. That ended our marriage among other things.