Documentation for clear title and home loan

Mother of Mr. A and Mr. A (Joint ower) have purchased a flat with home loan in 2005 and family member of Mr. A are father, Mother, one sister. Family member are residing in flat. Subsequently, father of Mr. A passed away in 2006 and Mother of Mr. A passed away in March 2010. Financial condition of Mr. A was very bad because mother was the only earning member and he was not able to pay society maintenance and home loan EMI. I have purchase flat from Mr. A in July 2010 and I was not aware of Mr. A family background and total family member at that time. I came to know about sale of flat through property broker. All agreement drafting and registration done by broker and agreement got registered and I also took home loan from NBFC. Agreement registered between Mr. A and Me, agreement silent about death of mother of Mr. A. I have death certificate of mother of Mr. A. No one raised any concern about will of mother, legal heir NOC or search report etc. I am residing in same flat from the day I have purchase. Property tax, electricity and share certificate of society transferred in my name. Now I want to transfer my home loan from NBFC to bank, then they has raised question 1. Will of deceased person 2. List of legal heirs 3. NOC from legal heir 4. PUBLIC NOTICE & NO CLAIM CERTIFICATE ISSUED BY ADVOCATE. Please suggest me document to be prepared as on date to avoid this type of observation Also suggest that is my right on current flat will get affected because of non-availability of above document?