Property Agreements Query

My  aunty  having  Flat  at  Bhayander  east, living  with  One  Son  and  One  Daughter . Her  Husband had  died  very  long back  .This  flat  was  not  registered  and  also  not  paid  stamp  dutyat the  of  his  expirered.  But  after  husband  died  society    was  transfered  her  name in  Share Certificate.  Now  to  pay  registration  fees  and  stampduty .  lawyer  advised  that  do  release  document  in  her  name .  After  release  document  if Aunty dies  then  who  will get  ownweship rights.  Shall  son  or  daughter  will get  Ownership  right  or we  have  to  prepare  Indemnnity  bond for nomination,  please  advise us