Does a woman have any rights in in-law's property

Dear Sir, We were two brothers and two sisters each. My father died 25 years ago. My elder brother passed away in 2013 while my mother passed away in 2015. Before passing away my mother made an unregistered will signed by two witnesses, stating that all her movable-immovable property will be given to me and one of my sister in equal portions. The other sister has not claimed whatsoever. However, my deceased brother's wife has given an application in the municipal corporation for enrolling her name in the house which we live on the basis of succession. They have started the process without giving any notice to us. I asked a few people about this and they said that my brother's wife has full right for it and no one can stop her from being enrolled as a co-owner of our house. Meanwhile, I searched for laws and acts related to this and found that she has no right whatsoever on this property. This house in which we live was first a piece of land bought by my mother through proper registry on stamp paper and the she constructed the house over it. I just wanted to know how can I stop her from being enrolled as a co-owner of this house. What measures I have to take and where to appeal to stop this process. Thanking you in anticipation