Agri land case

Hi, below im geving case u details, plz give me advice. My great grandfather has 2 sons A and B...... A and B (b is my grandfather). After the demise of my greatgrandfather i.e in the year 1975, he was servived by A and B mentioned above who was allotted with a piece of land. A was allotted with land survey number 100 and B was allotted with land survey number 101. But both were cross possessed i.e, A did and after him his descendants are doing farming activities on land 101 and vice versa.after the demise of A his decendants are still carrying on agriculture on the same land i.e 101 that too since 1980. Over 34 years they are enjoying uninterrupted access over land 101. Over a period of time thereafter my grandfather B also died are we his decendants are enjoying uninterrupted access on land number 100 for over 19 all of a sudden objection has been taken by the son of A that lands should be given as per the actual allotments.they are doing so because the lands which they are cultivating is about to loose its fertility as is about to become less productive. My question is what can be the legal remedy for B?