Right to property

From ur question it seems that will is regd., during the life time of your mother.  Date of regn., of will and date of death of ur mother is important.  If you have any doubt regarding the signature of ur mother, then you challenge it in the court.  Unregd., and regd., will can be challenged.

1- The Will deed can be Registered after the Death of the  Executant !

2- if you are disputes the Will deed  7 You have doubt aobut the Will Deed , You have  to claim  your share in the proerty by filign  suti for parrtition - ignorign he Will & ingoring the Ppaer Notice  as you are not in india  , if yoru brother claims exclussive rights on the proerty on the basis of the Will deed -he has to  prove the Will Deed,  execution of the Will deed by your mother   and that she was in sound state of mind and disposing state of mind and that there was no force .  It si burden of  your brother to prove the Will deed - 

3- File  Suti for partition stating that your mother died intestate (i.e;-  with out any valid Will Deed )  and you are entitled to calim a share in the proerty as successor to her .