I had problems with my father-in-law for years. I've been ill for years with severe irratible bowel syndrome, chronic fatigue, and a sleep disorder. As the years went by, my health continually became a problem in holding employment. The only person in my family convinced I was a faker was my Father-in-law. He would constantly berate me in front of my children, tell me I was lazy and it got to the point where I had to kick him out of my home.
I told him that I would not tolerate him disrespecting me in front of my children, and my wife backed me up (I love my wife so much, she has been so supportive to me). We both told him that unless he could learn to respect us as adults, and keep his disrespect to himself, he was no longer welcome to visit his grandchildren. Over the years, he has seen that I'm not actually lazy, just exhausted a lot, and he has seen me take care of my fatherly and husband duties round our home. Eventually, he came around and apologized, and we get along pretty well now. When it comes to difficult in-laws, this is my advice:
1. When you married your spouse, you married his/her family as well. It is part of your responsibility to look past their flaws and love them anyway. DO NOT seek revenge for slights against you by your in-laws. Be the bigger person, tell them in private about how you feel without stooping to name calling or back-biting.
2. Stick to your principles. If in-laws are very belligerant towards you, stand your ground and tell them they are not welcome to visit you/kids unless they can respect you in front of the rest of your family. Sometimes, love needs to get tough.
3. Talk with your spouse about the problem. Its important that your spouse back you up with in-law problems, as dealing with them alone makes you look like an idiot. Spouse cooperation and support is VITAL when dealing with difficult in-laws.
Things between my Father-in-law and I are not perfect, but he tries now, and if he says something disrespectful towards me, I gently remind him, in private, that respect is earned, not given. If he cannot respect me and the fact that I have health problems, why should I respect him? He's a good man, a bit self-centered, but he loves his family, and I never stop trying to improve our relationship, as I know that its important for our family to get along.