Sale of property but later will found forged

I have been offered a plot of leasehold land in Kolkata, wherein the following have come to my notice: 1. The original lessee died in 2003, leaving behind his 5 legal heirs, wife, three daughters and a son. The deceased was by faith, a Hindu, in case Hindu succession laws are reqd to be referred. After his death, the property got mutated in favour of the above five. 2. In 2006, one of the daughters died, leaving behind legal heirs husband and a daughter (minor till date), and in 2009 the wife of the deceased also expired. Now, the interest in the plot remained as under: 25% each with 2 daughters and a son, 12.5% each with the husband and minor daughter of the deceased daughter. 3. In 2013, they say that they have found a will made in the year 2000, favouring the son only i.e. entire plot in favour of the son, the will has already recd the probate from the high court. The will is limited to this particular property only and no other asset has been referred to. Althought mutation is pending, the land officer has served personal hearing notices to all the members and they have signed in the land dept office also in their own handwriting. All the members whose interest are getting ceased are ready to sign on all papers. Now following are my concerns: 1. Will: The fact that a will has popped up 10 years after death is something not easily acceptable. The members who are losing their interest have made representations in court and registry dept, but in future can they challenge the will on the grounds of: a. Non citation b. Deceased signature was forged c. Deceased was influenced, or was not of sound mind d. A supplementary will is again produced since there is a considerable gap between the will (year 2000) and death (year 2003) e. The will was barred by limitation f. The people whose interest are getting ceased, there signature was forged Further, lets say the will turns out to be fake one, and the members losing interest have no knowledge of it today, although they have made representations and are willing to sign further also. In future they have come to know this fact, and now are challenging the will on the ground that the will was fake and it was not known to them earlier. Whether a declaration to the effect that members losing interest are satisfied with the will and in future they will not challenge the said mutation on all the above grounds i.e. non citation, will forged, undue influence of testator, a supplementary will, that their signature was forged, would suffice. Also some payment made to them would be good enough consideration so that in future they cant take legal action. Whether such an affidavit in front of F.C. Magistrate and a doctor will hold good in law and is good evidence for the future? 2. Now further if we enter into agreement with the new owner, the son, what safeguards should one take so as to secure the money becuase 90% money will be paid on possession. 3. There is a minor whose interest is getting ceased, how will that play above. Are we reqd to make any deposit for her, or it is the responsibility of the father who is also the natural guardian. I am a bonafide purchaser, how can I protect myself keeping in mind that they are ready to sign on all papers today. A reply would be highly appreciated from the experts. Pls provide the much needed guidance. Pls do cite case laws similar to the above case.