Sale deed executed to two party

Mr.Jeevan, 

Please note that the transactions between A, B and C are all fine, first sale deed between A and B holds good, no one can challange that since B having a title deed, then as Mr.Balaji asked what about the Encumbrance Certificat in which one can find the genuintity and other transaction details happend in a particular Survey Number, so in case of C stating that he is not aware of the sale between A and B  the same reason can not be taken as a valid stand moreover C can only get remedy from A not from B, since there is an indemnification in case of convey the title, another one is Possession in your statement the two transactions between 2000 and 2010, so it is not coming into adverse possession also hence if the B's Sale deed is genuine and effectively reflected in an Encumbrance Cerifitcate then no one can challange his title, one thing important atleast now itself B has to act immediately  for getting patta name tranfer in his name otherwise he might be in trouble to prove his  possession. 

The first  transferee will be the legal owner in your  case  his  title  can  only  be  defeated by successfuly  proving  advrse possession  the first  transferee  would  not be  bound by  the  subsequent  sale  deeds.