Ancestral house is build on a land for which only an agreement on a stamp paper exist

I stay in a house in a joint family system. My grandfather had 4 sons and all 4 of them along with their family stay in the house.

All 4 brothers were involved in a family owned grocery shop which was on rent. In the past the shop ran well and was enough for all of us. Recently for the last 5 to 7 years there is meagre sale and it is difficult to support 4 families. This caused a lot of debt and of financial trouble.

The house where we stay is on a piece of land which was bought by my grandfather some 50 years ago. No legal document exists for the transaction except an agreement of sale on a stamp paper between my grandfather and the seller.

My whole family built a house on it then and we all are continuously residing in it since almost 50 years. We have electricity bill in the name of our grandmother. My grandfather has passed away and so is the seller of the land.

We never received any tax due receipt or property tax receipt and we have never paid the same.

Due to financial crisis we want to sell the property- house along with the land parcel but since we do not have any documents we are not able to sell it.

What can be a solution for us to regularise ownership in our family’s name so that we can sell it.

Please advice and guide 🙏