If you have in-laws who seem cross the line a lot, here are some constructive strategies for dealing with them.
Don't assume they are intentionally trying to be difficult. In many instances, people think they are being helpful. They don't realize that dropping by unannounced or giving unsolicited marital or parenting advice is not appreciated. Get with your spouse and brainstorm things that your in-laws could do that would be helpful. Then sit down with your in-laws and talk about what you would appreciate them doing. Also discuss things that you would like them to stop.
What if you believe it is truly unhealthy for your family to be around your in-laws? Your first responsibility is to your spouse and family. If being around your in-laws creates safety issues or requires you to put your family in an unhealthy environment, you'll want to set limits. When you know you'll be with your in-laws, decide as a team how much time you will spend there. Perhaps a code word or signal that the tension is mounting and it is time to wrap up the visit would be helpful.
Be careful about anticipating how things will be. In many instances, anticipating being around difficult in-laws can increase tension and actually make the situation worse.
Stand your ground. Many couples experience marital distress because one spouse doesn't want to hurt his/her parents' feelings and doesn't see how them "investing" in the marriage is harmful. If your spouse is uncomfortable with how the in-laws relate to you and your family, it is important to realize that the two of you are a team - not the two of you plus the in-laws.
Focus on those things over which you have control. You may try to do an extreme makeover on your in-laws' behavior, but in the end you will probably feel frustrated and discouraged. It might be better to focus on your own behavior and the things you do have control over, like:
How much time you spend with them
Topics that are off limits for discussion
How you allow their behavior to impact you