you have stated that BDA allotted site to seller .was the site on ownership basis or leasehold basis . ?
please clarify . . subsequently according to you seller sold property to you on lease basis for 10 years under GPA
. what were the terms and conditions of lease ? did it contain a clause as to renewal of lease ? was prior permission of BDA obtained? was there any clause in agreement that required prior consent of BDA before giving premises on lease?
if lease period has expired you dont have interest in said property . property cannot be registered in your father name .
it is necessary to go through the various documents cited by you to advise further . . if you are unable to trace the seller engage a detective agency . contact a local lawyer .