Need help regarding transfer of property

My dad died an year ago, we have 2 houses(same compound) owned jointly by my dad and his brother. The land where we built the house has been bought by my dad but he registered it in my grandmother's name. And my grandmother(alive) has written a will that after her death the house can be equally shared by my dad and his brother. The document is with my dad's brother, me and my mom have never seen that document and now when we asked for document they are refusing to give it. 1. Since my dad passed away and it is a kind of joint ownership will my dad's brother will be having full right's on the house? 2. What steps should we take in order to transfer name of the property(Dad's share) to my mom's name? 3. How to get the document from them?