Lawyer Opinion on sale of land

On 17/6/2006 our family members have signed the agreement (on Rs. 200 Stamp paper) on which it was stated that "we have sold 2 acres of land for 25 lakhs to my cousin brother and we have received 24 lakhs and 50 thousands in hand (in cash) and remaining 50 thousands will be paid during registration. But we actually received only 2.5 lakhs in hand we do not have any proof during this agreement time and the agreement bond has not been registered at all. My Mother was expired on 4/2/2007. Please note that before this agreement this land was originally registered in my father's name (with a mutation copy from revenue department) who passed away on 24/4/1996. During 2014 i.e. on 30/4/2014 (after 8 years of agreement) with the above copy of agreement my cousin brother has taken rights on this land with the approval from Thasildar and AC (revenue Department) without any registration. In registration EC form it has been mentioned that all my family members (including my expired Mother) have given the rights to my cousin on this land. In addition to this on 7/8/2014 my Step Mother (second wife of my father) & her son have registered the same land to my above mentioned cousin without considering signatures from me & my own sisters. As of now the sale deed (or the registration form) shows only my Step mother and her son's signature. Questions: 1. Is the agreement made during 2006 still valid now? 2. Can we fight on this case in court of law to obtain the land ownership since me or my sisters did not register the land yet to my cousin brother?