Conveyance deed

In Bombay we have purchase Tenancy Land  in 1973 form Farmer  in name   Samtanager Co-op- Hsg Association  (GOVT. working group of 20 people) and Conveyance deed is sign by the only  6 people form our group . Before buying of  Land , we have not register    Samtanager Co-op- Hsg Association  with  Register to Co- Op- hsg. Society.

Presently out of 20 people 5 are dead. And we also do not have PAO for sign of 6 people on behalf of us  on Land conveyance  Deed.

 Due to this we are also facing difficulty to represent our Name on Property Card.

Now Relative of Land seller try to claim on land, can they do this???

They have file Objection with Tahasildar, SLR and BMC ?

Please guide us