Land sale dead dispute and challenged

Dear Sir, I had purchased a land in 2010 from Mr Raj Kumar Yadav who was then registered owner of that land as per Bihar land & Reform land register record and the same was also authenticated and verified through the LPC certificate issued by CO (Circle Officer),even motation has been also done correctly in year 2008.All the land related taxes were collecting on his name since year 2008 till our registration. Mr Raj Kr Yadav had purchased a land from a person (Ram Lakhan Yadav) who acquired registered POA from Late Sudhri Devi.Now this lady's family is claiming that the person (Ram Lakhan Yadav) who had acquired POA is fraud and get POA from another (unknown) lady as the registered lady was died on year 2003 so how could she give right of sale through POA to another person (Ram Lakhan Yadav) in year 2007. That lady (Late sudhri devi ) family has now made and producing a death certificate issued from district birth & death record state govt. authority in year 2014 where death year of this lady is mention yr-2003.They also showing the voter ID card of that lady which is not match with the lady's pic pasted on registered POA given to Ram Lakhan Yadav. Currently Ram Lakhan Yadav is died in a road accident and family of late sudhri devi has filed criminal case at district civil court under JM and framed all the charges of conspiracy and criminal act on me as well as on Mr Raj Kr Yadav (including witnesses signed in all sale dead & POA) for acquiring and getting possession of this land by unfair means. We have constructed 3 floor building on this land (construction completed on yr-2012) which they also claiming that they have made this construction and we are holding this forcefully.We have all the constructions related bills and contractor & labor all are ready to be a witness for this. DSP of our area has completed his survey and has also found the constructions has been done by us after inquiry with our neighbors and same he has written on his case diary.Since yr-2012 till now we are paying house taxed to municipal and also paying electricity bill since 2011.All the connections are registered on my name and bills were collecting by my name. I would like to mentioned that through a certified copy of sale dead of late sudhri devi we found that no identification has been registered/marked on official document (neither Photo not any signature or finger print expressions). Now i would like to know the probable final verdict of court in this case considering all the facts- 1.what are the key document required to prove that the lady who had given POA is not the same who actually was the registered owner. 2.if somehow they managed to prove the above point then what court will decide.Will court consider our constructions related expenses and conspiracy against us as we would also become a victim of fraud done by Mr Raj Kr Yadav. 3.Will court consider the fact that whatever that state govt has verified/confirm to us as per their confidential document and record we had done and purchased land accordingly.where is our fault and what mistake we have done. I would like to request you all Law genius people to help me out with you valuable guidance and suggest path which we should follow to protect our right and invested money. regards, Saurav Kumar