There are two separate plots properly recorded in the revenue records. Plot A is in your possession which is comprising of twenty decimals. The whole twenty decimals are in your possession. Ownership on plot A is undisputed because you have been in possession for fifty years.
Your possession is peaceful because your neighbour has never assailed ownership till 2010. However, he is claiming owner upon four decimals land after your father’s death, but he did not initiate any legal proceeding against you.
File injunction suit as soon as possible
In this circumstance you should file an injunction suit as soon as possible. Your neighbour has no right to demolish any construction erected in your land. He has no right to interfere in your possession either directly or indirectly. So, you should stop him to interfere in enjoyment of right by filing injunction suit.
The court will grant ad-interim relief and preclude him to demolish any construction till the disposal of civil suit. Thereupon he cannot threatens to demolish your property or cause unnecessary disturbance. If he does so then you can immediately approach the court. The court will stop such acts and ask surety from your neighbour.
File declaratory suit
In this condition you should get declaration from the court that you have exclusive ownership over the plot A. This right is essential in the current circumstance. Declaration from the court will exclude all the person to claim right, title or ownership on your plot. Hence, it is mandatory to file a declaratory suit against your neighbour.