Purchase of 999yrs lease land

Please advise if 7/12 form has no names mentioned on it for mercy land(khar land) Person A says that he has this land is on lease for 999 years. At present its in residential area Can person A sell this land and can this land be purchased by us legally. Also advise if we can convert this land from residential zone to commercial zone. Also is it possible to become owners of this land forever. Please advise.