Property dispute b/w widow and sisters of her died husband

I am posting my friend's case here ..

Pls read and post ur views,as it deserves humanitarian aspects.......

Mr.Santhosh(who died recently),married & 50 years at the time of death, belongs to Christian Community and has no lineal discendants but kindred(i.e 3 sisters)...His father and mother are also deceased...Mother was died recently 3 months before Santhosh's death..The three sisters had received their share earlier from parents and gave their assent in an agreement they won't claim further in future... Now a civil case is running in the court between 3 sisters of him and Santhosh's wife,which was actually filed by the 3 sisters after the death of their brother....There is a registered will deed(registered on 2006) of Santhosh's mother that after her death,her entire property is entitled to her son i.e Santhosh only..But,due to Sub registrar's error there is only one attesting witness and two identifying witnesses in that will..This was unnoticed and the advocate of 3 sisters pointed this error and asked the court to cancel the will due to this reason.Is there any chance that 'will deed' will be cancelled by munsif court,due to this single reason?
If will deed is cancelled,what would Santhosh's wife will get...?
If will deed is valid,what would Santhosh's wife will get?
I might think this case will be as per Christian Succession Act..
Express your views as early as possible..