Mother in law mentally unfit, father in law sold property, what to do?

My father-in-law married before 25 years ago, My mother-in-law is mentally weak but she can do any kinds of work, but she cannot think much more. After marriage, my father-in-law did not keep my mother-in-law, he kept only for some occasion/function. Both have only one daughter, that is my wife. My mother-in-law is also a single daughter of her mother & father, nor any other child. A few months before my mother-in-law's father had died, after death My father-in-law again married to other women without any family permission.My mother-in-law had no any issue because she doesn't have a mind to think. Then after my mother-in-law's mother write all property to my wife as a cell deal. After a few months my father-in-law sold 50% of all property through my mother-in-law. Then What Can I do the next step? - /