Yes, it wouldnt make much difference. All sons of the party in question could claim ownership on the basis of the terms of the Will. It would however depend on the terms contained in the Will and further, the Will will have to be probated from a Court of competent jurisdiction.
Your claim to the proeprty would be barred by Limitation if you were aware of the existence of the property documents all along and as such, the documents to the property will be of no help.
You can file a suit or writ petition against BDA from interfering with your possession of the property and to restrain them from taking over the possession of the property without following due process of law or in the alternative you can file a suit on the basis of your title before the civil court in Bangalore.
It would depend under which act is the association registered. Is it the co-operative societies act or the apartment ownership act. The provisions of such act would have to be read with the terms of the sale deed and anything contrary to the act, would negate the terms of the sale deed and could invite litigation.
RERA registration is as per the date of completion entered by the developer for that particular phase/project registered with RERA, subject to acceptance by RERA authority