The unregistered agreement is not legally valid and cannot be enforced i court of law.

However since the other party is demanding the return of their property without honoring the mutual agreement between you both, and also since this will continue forever, it is advised that you better file a suit for declaration of your title based on the original oral agreement in the year and you can add the latest unregistered agreement along with other documents namely the patta, electricity connection related documents, tax receipts as documentary evidences to support your claim towards the declaration of title and interests in the property.

Submit an application to MRO under Section 4 of RoR Act enclosing documents of exchange. You need to deposit registration fee, and stamp duty on the  basis of value of property. A pattedar passbook will be issued to you. On the  basis of which  you can file a suit for declaration  and obtain a perpetual injunction against interference against your relatives.

it doesn't have any legal admissibility without registration. You can register it now also paying applicable penalty

The revenue records are not the title documents.

It may be useful to you to support your pleadings for declaration suit seeking the relief of declaration of title and interest to you  that has been advised to you.

Refuse to return the land 

2) let your relatives file suit to claim said land 

3) rely upon agreement entered into between parties for exchange of land 

4) passbook issued by revenue authorities for said land 

5) in event you file suit for declaration claiming ownership of land on basis of deed of exchange your relatives can take the plea that un registered agreement is not admissible in evidence 

Act as mentioned herein above 

- Since, you are already taken the possession of the same on exchange basis before the village heads in the presence of witnesses , then said relative cannot ask for the the same 

- Further, as you are in possession of that property since last 21 years , then even on the ground of adverse possession you can claim the ownership of that property. 

- Hence, you can file a suit for declaration before the court for declaring the legal owner of the said property and for getting relief permanently.