Obtain complete mutation records from begining: atleats showing ownership in the name of Father/ then in the name of brother by gift and copy of link document (gift deed) and then register the gift deed from brother to you.
Since it is gift between blood relation, the stamp duty/chatrges may be NIL/negligible.
If brother signs gift deed by appearing before registering authority,WILL is not required.
Will can be cancelled/changed by testator anytime in his life time.
Still if you wish ensure the WILL is valid and is signed by two witnesses and if possible register it.