It's good that you come here with your queries here. First of all you need to sort out the origin of problem.. You have to accept your mistakes also as well as you should not blame them also, if you really want to save your marriage. You need to go through detail counseling with your whole family.

I understand Ur problem. Most of the time it's due to problem in communication. Start listening to Ur mother in law to understand and not to answer back. Accept her the way she is as u would have accepted Ur own mother. Now listen to her without judging. I don't mean to say u r wrong and she is right. Once u listen to her with understanding then only u will get a solution. May be she is suffering from depression and needs help. It could also be u r behaving in a way from the perspective of a rigid belief. So seek to understand first before seeking to be understood.