What is the validity of the agreement on bond paper valid

Hi All i have a query regarding the property between 3  brothers. below are the details.

1. we are 3 brothers and  2 sister.
2. the property  under dispute was gifted by my great grand father under the condition my father dose not have the right to sell or morteguage the property,  the right of the property will be with the kids of my father.
3. we have buitl the new houes on the said plot in 2005.  and there is a housing loan on this property on 4 people, my father and 3 brothers as co-applicants for the housing loan.
4. my father had expired in 2007.
5. i am the second brother. and i had the agrement on a bond paper of 100 in the presence of the witness. saying i dont have any right on the property as i have taken money from my brothers for my education and other things. but still i am paying the my part of housing loan every month.
6. i dont want this property any more. but my wife is instigating to file a case on this property saying you have every right on this property. the agrement is not valid as it is not regeistered.
7. My question is. 
8. what more should i do to forfit my share from this property such that my wife will not any legal action causing inconvinece to my brothers and my family members.
9. pls do suggest the various options i have. to save this property from my wife.

regards 

victim