1) what was nature of agreement signed b6 your father with builder ?
2) is it registered ?
3) on father demise apply for mutation of property in name of legal heirs
4) enclose father death certificate , latest receipt of payment of property taxes
5) if you are unable to come down to India execute POA in favour of mother have it attested before Indian consulate
6) if no objections are received mutation would be done in name of legal heirs