For whatever reason, you are not under the same roof with her husband's parents, it is best to learn to live with them peacefully. Start by defining your space. It could be your room with her husband, or part of the house, depending on the area of housing. Insist that at least to some extent, to make this place their home. Of course, should not be venturing inconsistent with the rest of the tenants repair, but self-purchase of furniture already be a step to the arrangement of his corner, even in the parental home.
Distribute household duties. Decide in advance who and when cleaning the floor in the common areas, use the washing machine. Many serious conflicts begin with household trifles.
Try to negotiate with relatives spouse comes to you guests. If you suffer from tightness best to meet friends outside the home - so you get rid of an extra reason to quarrel.
Do not be too open to new relatives. We should not complain about them to her husband, even if you had a falling out. Firstly, they are likely to stand at his side. Second, it can only exacerbate the conflict with her husband.
In all his actions and deeds try to proceed from the principles of mutual respect. Conflict is bad for everyone, so sometimes should concede at least to maintain calm in the house.