Property Issue, As we continuously living 20 years in house

Hi, Please go through the below details Family tree A - First Elder Sister Unmarried (Died) B - Second Elder Sister Married(Died) having One Daughter and One Son C - Third Elder Sister Married(Live) having One Daughter and One Son D - Brother(Died) of above Sisters - Two Sons This is Present Status ========================================================= A - has some liquid cash and a house as property in her name A - has distributed the liquid cash to her younger sisters ( B and C ) and house to her brother( D ). when A was live. A - Did not write the house in Brother Name ( D ), Presently the House was in A Name D - has been living in that house from past 20 years continuously by paying the tax ========================================================= B, C - came to know still the property was in A Name Now they send a lawyer notice to D (died) sons, stating that they(B,C) have the equal share in A house property. ======================================================== Question: How can D (died) Sons can acquire that A property in their name, who living from past 20 years. if a person living in a house for 12 years continuously, he can claim the owner rights ...if it is yes, how it can be in legal. Can you please suggest and guide for the above mention things Eagerly waiting for your response. Thank You, Vidyasagar