Legal info about purchase of old house and constuction of new house

I trying to purchase a old house 2 floor 1800 sft  built-up  on 30x45 site. It is BDA site allotted to X  through LCSA in 1981 and cancel in 1985 BDA allot same to  Y in 1985 though LCSA for 1985 followed by conditional Sale deed for 10 years. Building sanction taken in 1985 and build with in 2 year.  In 2000 applied for  Absolute sale deed. But BDA  just provide a Notice reply saying To treat  Conditional sale deed as absolute sale deed. In 2001  Mr X sold to  P In 2009 Mr P sold to Q in 2015 Mr Q sold to R In 2019  I am planning to purchase Katha was issued by BDA later BBMP to all the owners. Property tax has been paid regularly. EC shows the all the transaction My question is :   Is  Notice issued by BDA is valid endorsement for Absolute sale deed.  and my current registration is legally correct. Can I  demolish the old building and construct  new duplex house. What is procedure to get demolish and new construction. Thanks in advance vijaya kumar GS