Ownership of Apartment after death

My wife (75 years old) and me ( 79 years old) are joint owners of apartment in central Chennai. We are Green Card holders due to compelling circumstances to be with our daughter. We are a bit concerned whether our son & daughter who are citizens of US will have the patience & tenacity to sell the apartment on death of both of us following complicated procedure of probate, legal heir, etc.We are thinking of going back to India & stay in our apartment itself. I require the following clarification: 1. Is probate necessary? By giving an affidavit now or registering a Will, can this be avoided? 2. Will a Legal Heir certificate be required? Can this be avoided or substituted by giving an affidavit now or registering a Will? 3. Is there any provision to register now the transfer of the ownership to either our son or daughter after five years or any similar scheme? I request learned Lawyers who are well aware of Tamil Nadu provisions & more specifically Chennai to give their kind suggestions..