Authenticity of unregistered WILL

I am hindu & have a unregistered WILL of my father for his self acquired property. He intended this will (died 30 years ago), got it written by my maternal uncle & signed it. WILL was also signed by the same maternal uncle & his wife as witnesses in presence of my father. After my maternal uncle's demise (20 years ago) my aunt handed over the WILL to me. My step brothers then started questioning authenticity of WILL claiming it was written by my uncle in their absence. I have now decided to approach court for share of my father's property on the basis of WILL and I have following questions. 1) As WILL is unregistered, do I need to first file a probate suit OR can I file a partition suit using this unregistered WILL ? 2) As WILL is unregistered, is there anything my maternal aunt (only living signed witnessee for WILL) can do to prove authenticity of WILL? if yes, how can I get it done quickly as she is now 80 year old and sick. If no, how else can I prove the authenticity