Money transferred of a very ill person

My father was died on 20th September 2016 at Uluberia,Howrah.I am only child of my late parent (my mother was died a few years before). In the last few month's my father had been suffering from acute kidney problems ,actually had to dialysis thrice in a week. He was a patient of blood sugar from his middle thirties or early forties.  My late father are 9 brother and sisters . In the last few months my father was under one of my uncle and aunty. After death of my father I found that some large amount of money was transferred from my father's account   to that  aunty account and bank confirm the same just few weeks or days or may mostly a month before my fathers death. But as I know my late father's mental state of health was very poor since he was severe kidney,blood sugar and other related problems and  he could not do his daily duties if he was not helped by a person.I am the joint account holder of the above account. My name is Tanaya Das (Husband Suva Sankar Das). Since  I am married and lived a quite distance from my father I could not attend my father . now my humble questions are in the folloing 1. How bank transfer the money of such person in such a state without informing me ? 2. Can I make a case against my uncle and aunty and bank both ? 3. How can I establish  my  argument in the court and can court accept my point ?   It is possible for me to recover the money lawfully ?