Second registration fradulently done on a plot in hyderabad

Sir, My mother purchased a plot in 1990 and got it registered in her name. In 2017, when my parents wanted to build an independent house, we get a call from the second buyer that he purchased the same land in may 2017 for 70 lakhs. On the registration papers, we see 14.5 lakhs. The registration was done on 18 th may 2017 in balanagar registrar office, hyderabad. When we ourselves observed the registration papers, we found different photos of owner in aadhar card xerox and on the day of registration. When we saw those papers, we saw seal around each photo was missing and on the document dated 17th may, office seal was 5th may. The buyer 2 obtained EC too and could do online registration too. Without this knowledge, my parents applied for EC, we also obtained EC in my mother number. When this transaction was done in 1990, Power of attorney was given to Mr. Narasimha Reddy by his brother who was the actual land owner Mr. Chandra Reddy. But the buyer 2 papers shows that the owner of land is Narasimha and Chandra Reddy mother and she passed onto her grandson Raghava Reddy who is Mr. Narasimha Reddy. Multiple visits by my father to meet the actual person Raghava Reddy failed as he was not at home but Mr. Narasimha Reddy gave 2 versions initially he does no and on another day, in phone told his son Raghava Reddy sold to buyer 2. The registration paper dates and office seals are not as per rules. So we concluded it is fake, The buyer 2 started with negotiation with my parents asking them to give off land for 15 lakhs. Its actual worth is around 50 lakhs. Later he says he can give 30 lakhs. My parents want to proceed with boundary wall and see if they witness any problem from buyer 2. They want to keep an escort from lawyer for protection. They also want to take cuviet so that before filing case in court, buyer 2 has to inform my mother who is buyer 1. The same balanagar register office registrar and subregistrar were suspended on may 31st for fraud. On the same day, the chief minister of Telangana cancelled online registration system. We are confident that the second registration was fake after going through the documents. Can we proceed with boundary wall . We want to see if buyer 2 causes any obstacle or proceed legally incase of problem which my parents witnessed or if buyer 2 himself files a case in court. We are delaying court case as my father is retired 66 years old and my mother is 61 years old. Both of their daughters are in other states with young kids. So it will be difficult for family to run around court and get back the land or cancel his registration if done. Please tell us what can be done so that we can stop buyer 2. We also want to personally go to registrar office balanagar and check if this registration of buyer 2 was done on may 18th, 2017. We want to see the records as online registration was proved to be fradulent. Please suggest keeping in view of my parents old age.