What is the process of selling my inherited flat in mumbai having unregistered agreement of Dec 1983

Hello, I have inherited my mothers (deceased on 17.12.2005) flat and 100% Share has been transferred in my favour by the society with all interest on the basis of 1.Application for membership submitted by me on 20.09.2013 along with copy of death certificate. 2.Copy of my mothers nomination form in my favour dated 15.09.2004. 3.Cheque of Rs.500 towards share transfer fee - dated 24.08.2013 4.Cheque of Rs.100 towards Membership fee - dated 24.09.2013. 5.Notarised indemnity bond on Rs 200 stamp from me to the society mentioning my sibling (sister) and me as the only legal heirs to our mother. 6.Notarised affidavit and undertaking on Rs.100 stamp dated 19.09.2013 - from my sister relinquishing her right and interests and claim, acknowledging my mothers will of bequeathing her (my mothers) right solely in my favour, giving her irrevocable consent and NOC to the society and any other statutory authority to transfer the rights title & interest solely in my favour in her sound state of mind . 7.Common form no.4 from me to society. In addition i also have my mothers, a. NON registered/probate/ notarised WILL & TESTAMENT on Rs.20 Stamp dated Sept 2004, keeping me executor of the WILL, bequeathing her share, title, right interest of the said flat in my favour. And a b. Notarised Family agreement dated 14.04.2004 executed on Rs.20 stamp between me, my sister and mother . The above process of transfer of shares and interest was carried out as advised by our societies auditor & C.a & lawyer and the will and family agreement as advised by my mothers then lawyer. The original agreement is of Dec 1983 and is not a registered doc since property was acquired (dec 1983) before stamp act came in place. Infact when amnesty scheme was announced i submitted my documents for registration but they didnt go thru since they couldnt handle the high volumes of non registered agreements receievd by the bandra registeration office back then (around 10 years back) and since then no effort was made by me to get it registered or stamped. I have been enjoying the complete rights, title ,possession, interests with all necessary bills of electricity ,ration card ,society maintenance and all 5 shares being transferred on share certificate etc in my name Now i am interested in selling this property . I would like to know how will the registration process happen since the agreement is not a registered document and can i transfer my rights to any prospective buyer on the basis of the above transfer process. NB: My mother was a Muslim married to my Hindu father with me following my Mothers religion and my sister born as muslim and named muslim but changed her identity to hindu with change of name etc.