A person hand-picks their spouse, knowing they get along great with them. That is not the case with your in-laws, however. They come along as part of a package deal. Arguments or tension with your in-laws can lead to problems with your spouse in the future. An effort can, and should, be made to have a better relationship with your in-laws and prevent a family feud down the road.
The first step in improving the relationship with your in-laws is to accept the fact that you can't change them. When someone has behaved one way their whole life, they are unable to change. The best thing to do is change your reaction to their behavior.
Distance yourself from any fights or feuds that are occurring between your spouse and her family. Involving yourself only adds fuel to the fire. When the family feud comes to an end, you will end up looking like the bad guy and, depending upon the character of your in-laws, that might not ever change. It is normal for families to bicker but, in order to maintain a decent relationship with your in-laws, you should stay out of it.
Getting to know your in-laws as people, and not just as your mother-in-law or father-in-law, takes considerable effort. It will be worth it in the long run though, and you might just discover that you actually like them. Try inviting them to lunch or dinner, where you can talk without being sidetracked. Make the call yourself, so it doesn't seem like it is their son or daughter's idea.
Even though it may not seem like it, there is a good possibility that your in-laws feel awkward around you as well. This can cause them to treat you with indifference or hostility. Try to ease this awkwardness by making them comfortable in your home. Offer them a drink, involve them in conversation and try not to avoid being around them.
There are occasions where people distance themselves from their in-laws, because they feel they may be betraying their own parents. There is no harm in loving both sides of your family. A good relationship with your in-laws will only lead to a better relationship with your spouse. If this is a feeling you can't overcome, it may be a good idea to seek counseling. There could be deeper issues that need to be explored.