Registered will and subsequent unregistered will

the latest will holds more value even if unregistered.

In my case, there is a registered will written in 1998 by my Dad and he gave four properties each to all four children in that will, and I am the last son among four children.  All three of us have no issues.  When I was not in India and went for job, my elder brother(AAA) who is a drunkard and has no job borrowed money from gundas and had to force my Dad to sell to that gunda one of the four properties that was written on his share in that will.  Later he threatend and forced my Dad to write a settlement of two of the remaining three properties on his name.  As the elder brother(AAA) was living with my Dad in our ancestral home, and our Dad was very old, he succumbed to AAA's pressure and without informing me or other children, he gave that two properties as settlement to this problematic elder brother(AAA) back in January 2006.

A month after he wrote this settlement, in February 2006 he passed away under mysterious cirumstances, which all in my family didn't want to poke in to, for we don't have any proof of evidence to accuse anybody.  Its only after I came back to India for my father's funeral, I found out that AAA had forced our Dad to write this 2 property settlements and one sale deed of a property which are already in AAA's name in the Will.

My doubt is, would AAA might have obtained a signature from our Dad in a blank paper and may rewrite a new will on his own taking my share as well or have had forced our Dad to re-register another Will.  If so, how would I find it? And if found that, that is the case, what remedial measure could I take to avert an unlawfull hostile take over of my property by this unscrupulous greedy elder brother(AAA). 

Please advice me.

Thanks.

Venkatesh