Registration on same plot which twice how can 1st party claim

 My mother now 61y registered a plot in 1990 . In 2017, when my parents get a call that Mr. XX registered the same land on 18th may 2017 . On the papers, we see different value. The registration was done on 18 th may 2017. When we ourselves observed the registration papers, we found different photos of owner in aadhar xerox and office photo. When we saw those papers, we saw seal around each photo was missing and on the document office seal was 5th may. The buyer 2 obtained EC and online registration showed. we got EC after him. In 1990, Power of attorney given to Mr. XX by his brother who was the owner Mr. YY. But now XX son transacted the deal. But proof not known as XX says dont know once and says my son dealed it. others absconding. Can we proceed boundary wall construction and after witnessing any trouble file a criminal case or wait for buyer 2 to file as his papers are fake. buyer 2 wants to give money. what to do?