Incorrect survey/hissa number in sale deed

I have a plot which was bought by my late father around 20 years ago. The plot was registered to him through a GPA holder of the actual land owner. Later, we lost about 50% of the area of the plot to the NICE express way road and the only way to access the property was through a bridge on the storm water drain adjoining the property. I have two problems now. - The survey hissa number mentioned on the sale deed is incorrect. The actual number mentioned is now acquired by the express way. We are in possession of the property with an electricity connection for the last 15 years. The GPA holders have passed away and we are now in touch with the land owner. However, the land owner does not have this area registered in his name since it is an ancestral property and the division of land has not happened yet. Due to this, there are several family members involved and getting a consensus and rectification deed has not been possible even after several years of pursuit. - The access road as per the original plan is now not available due to the highway on one side and an apartment on the other side. We are left with less than 6 feet to access the property now. The plot opposite the entrance was empty all these days, but now there is a construction planned there. Please advise if there is any legal option to get the sale deed rectified and options available if the plot becomes landlocked.