Civil suit for cancellation of registered gift deed

It is a civil suit. A lady at the age of 68 years executed a registered gift deed in year 2002 in favour of her youngest son who was residing with her/ parents. The done executed the said gift deed in year 2004 by constructing floor on gifted portion. However in year 2013 , the lady filed a civil suit for declairing the above said gift deed executed in year 2002, as null and void. In the civil suit, the lady says that in year 2006, she came to know that the above said gift deed executed by her in year 2002 was fradulentaly done and being senior citizen she could not file the suit for 7 years from year 2006 ,since she came to know of fraud, till year 2013 when she filed the case. During initial arguments the judge observed that it is clearly time barred as per article 59 of limitation act. The lady/ Plaintiff expired in year 2014. After the death of the lady/Plaintiff, two of her eldest sons became LR1 and LR2. The youngest son in whose favour the gift deed was executed remained as Defedant. To avoid time lapse as per article 59 of limitation act, LR1 and LR2 have sought amendment under order VI of Rules 17 saying that they have come to know about the above said gift deed only in 2013 and therefore the original submission by Plaintiff that she came to know about the fraud in year 2006 shall be replaced by their new assersion as amendment. Now question is Can LRs change the original petition of plaintiff after her death by seeking such amendments. If allowed so, the Defendant shall lose the accrued benefit of time lapse as per article 59 of limitatiom act and it is detrimental to his cause. Should such amendment be allowed under order VI of rules 17. Presently arguments are being heard about sustainability of suit under article 59 of limitation act.