Amongst many families today especially where in laws are involved there is something very important lacking. That is justice.
It is so important for each member of the family be just in their treatment. The main issue generally arises between the mother/sister in law and the daughter in law. These isues can lead to a lot of hurt and stress for those involved. It can cause stress between son and mother and between husband and wife relationship.
If everyone was just in their treatment of others there would be much more harmony in these relationships.
The daughter in law is not inferior or the maid of the family. She should be treated with respect. She is not obliged to serve her in laws and should not be forced to do so. In the same way the mother in law should be respected and treated in a kind manner.
Most importantly it is necessary for the husband to be just in his treatment especially when problems arise. He should not blindly just side with one or the other. But look at both views and ensure that no one is treated unjustly. Speak to both of them kindly but do not allow one to transgress the other.
Although it may be difficult at first to do this it will eventually become easier and in the long term allow people to live more harmoniously with one another.